Controller having tag encoder for printhead

ABSTRACT

A controller for a printhead is provided having an encoder for encoding tags to be printed on a page. The encoder has an input at which to receive a tag structure template having at least one predetermined mark position, an input at which to receive fixed data bits, an input at which to receive variable data bits, and a dot generator which uses the input tag structure template, and fixed and variable data bits for outputting, for at least one mark position of a respective tag, a single bit indicating if a dot is to be provided at the at least one mark position, for the respective tag.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of US application Ser. No. 12/506,241filed Jul. 20, 2009, which is a continuation of U.S. application Ser.No. 12/138,359 filed Jun. 12, 2008, now issued U.S. Pat. No. 7,575,151,which is a application is a continuation of U.S. application Ser. No.11/738,518 filed on Apr. 23, 2007, now issued U.S. Pat. No. 7,398,916,which is a continuation of U.S. application Ser. No. 11/248,435 filed onOct. 13, 2005, now issued U.S. Pat. No. 7,222,780, which is acontinuation of U.S. application Ser. No. 10/296,535 filed on Nov. 23,2002, now issued U.S. Pat. No. 7,070,098, which is a national phase(371) of PCT/AU00/00517, filed on May 24, 2000 all of which are hereinincorporated by reference.

FIELD OF INVENTION

The present invention relates generally to methods, systems andapparatus for interacting with computers.

In more specific terms, the present invention relates to the formattingof a coded tag, a tag to be added to a printed page during the printingof the page, and a tag encoder to effect the production of tags inaccordance with the format. The tag encoder is particularly able to beimplemented in a print engine/controller by which to produce printedpages incorporating tags, along with other graphic and textual matter.

The invention has been developed primarily to allow a large number ofdistributed users to interact with networked information via printedmatter and optical sensors, thereby to obtain interactive printed matteron demand via high-speed networked color printers. Although theinvention will largely be described herein with reference to this use,it will be appreciated that the invention is not limited to use in thisfield.

CO-PENDING APPLICATIONS

Various methods, systems and apparatus relating to the present inventionare disclosed in the following co-pending applications filed by theapplicant or assignee of the present invention simultaneously with thepresent application:

-   -   PCT/AU00/00518, PCT/AU00/00519, PCT/AU00/00520,    -   PCT/AU00/00521, PCT/AU00/00522, PCT/AU00/00523,    -   PCT/AU00/00524, PCT/AU00/00525, PCT/AU00/00526,    -   PCT/AU00/00527, PCT/AU00/00528, PCT/AU00/00529,    -   PCT/AU00/00530, PCT/AU00/00531, PCT/AU00/00532,    -   PCT/AU00/00533, PCT/AU00/00534, PCT/AU00/00535,    -   PCT/AU00/00536, PCT/AU00/00537, PCT/AU00/00538,    -   PCT/AU00/00539, PCT/AU00/00540, PCT/AU00/00541,    -   PCT/AU00/00542, PCT/AU00/00543, PCT/AU00/00544,    -   PCT/AU00/00545, PCT/AU00/00547, PCT/AU00/00546,    -   PCT/AU00/00554, PCT/AU00/00556, PCT/AU00/00557,    -   PCT/AU00/00558, PCT/AU00/00559, PCT/AU00/00560,    -   PCT/AU00/00561, PCT/AU00/00562, PCT/AU00/00563,    -   PCT/AU00/00564, PCT/AU00/00565, PCT/AU00/00566,    -   PCT/AU00/00567, PCT/AU00/00568, PCT/AU00/00569,    -   PCT/AU00/00570, PCT/AU00/00571, PCT/AU00/00572,    -   PCT/AU00/00573, PCT/AU00/00574, PCT/AU00/00575,    -   PCT/AU00/00576, PCT/AU00/00577, PCT/AU00/00578,    -   PCT/AU00/00579, PCT/AU00/00581, PCT/AU00/00580,    -   PCT/AU00/00582, PCT/AU00/00587, PCT/AU00/00588,    -   PCT/AU00/00589, PCT/AU00/00583, PCT/AU00/00593,    -   PCT/AU00/00590, PCT/AU00/00591, PCT/AU00/00592,    -   PCT/AU00/00584, PCT/AU00/00585, PCT/AU00/00586,    -   PCT/AU00/00594, PCT/AU00/00595, PCT/AU00/00596,    -   PCT/AU00/00597, PCT/AU00/00598, PCT/AU00/00516,    -   PCT/AU00/00511, PCT/AU00/00501, PCT/AU00/00502,    -   PCT/AU00/00503, PCT/AU00/00504, PCT/AU00/00505,    -   PCT/AU00/00506, PCT/AU00/00507, PCT/AU00/00508,    -   PCT/AU00/00509, PCT/AU00/00510, PCT/AU00/00512,    -   PCT/AU00/00513, PCT/AU00/00514, PCT/AU00/00515

The disclosures of these co-pending applications are incorporated hereinby cross-reference.

BACKGROUND

Paper is widely used to display and record information. Printedinformation is easier to read than information displayed on a computerscreen. Hand-drawing and handwriting afford greater richness ofexpression than input via a computer keyboard and mouse. Moreover, paperdoesn't run on batteries, can be read in bright light, more robustlyaccepts coffee spills, and is portable and disposable.

Online publication has many advantages over traditional paper-basedpublication. From a consumer's point of view, information is availableon demand, information can be navigated via hypertext links, searchedand automatically personalized.

From the publisher's point of view, the costs of printing and physicaldistribution are eliminated, and the publication becomes more attractiveto the advertisers who pay for it because it can be targeted to specificdemographics and linked to product sites.

Online publication also has disadvantages. Computer screens are inferiorto paper. At the same quality as a magazine page, an SVGA computerscreen displays only about a fifth as much information. Both CRTs andLCDs have brightness and contrast problems, particularly when ambientlight is strong, while ink on paper, being reflective rather thanemissive, is both bright and sharp in ambient light.

SUMMARY OF THE INVENTION

In one form the invention resides in a printed page tag encodercomprising:

-   -   an input at which to receive a tag structure template;    -   an input at which to receive fixed data bits;    -   an input at which to receive variable data bit records; and

a tag dot generator outputting single bits depending on position in thetag defined by the tag structure template and said fixed and saidvariable data.

A print engine/controller that includes the present tag encoderpreferably uses a high speed serial interface at which to receivecompressed page data. Page data may include contone image planes thatare decoded by a JPEG decoder and they may be scaled in thehalftoner/compositor under control of a margin unit. A bi-level imageplane may be decoded by a Group 4 facsimile decoder and it also can bescaled in the halftoner/compositor under control of the margin unit. Apreferably infrared tag encoder within the print engine/controllerserves to produce infrared data line by line in step with processing ofthe image planes so as to place infrared ink printed tags into a printedpage.

The purpose of the tag encoder is to place tags over the printed page insuch as way that they can be read at some later time by a suitable penor equivalent device. Each tag can be a 2D package of data (although thetag may be printed on an arbitrary shaped surface) that is to be writtenout and able to read later. Typically there will some data to be storedin the package that is written to the page, although sometimes the merepresence of the package of data (our tag) is information in itself. Withthe present tag encoder it is desired to write out lots of these packetsof data all over the page. The generation of these packets is controlledin any or all of size, structure, and how the data is stored inside. Thetag encoder and the Tag Format Structure (described below) gives thiscontrol.

The Tag Format Structure allows the tag designer to specify for a giventag which dots are printed as part of the physical printed tag structureand which dots are to be derived from the data. The data part of a tagis broken into variable and fixed portions. The fixed portions are thesame data for each and every tag on the page, while the variableportions are specified for each tag. One limit case might be that allthe data is variable, but just happens to contain the same value, thusmaking the data effectively fixed. Rather than force the user of theprint engine/controller (PEC) to supply data for each and every tagalways we allow the possibility of having fixed data for each tag.Exactly what data is in the tag will be completely application specific.One page may have tags that contain X/Y coordinate of the tag as thevariable data, and a page id as the fixed data component. A pageinteractive pen (or equivalent) could subsequently read thosecoordinates back from tags on the page and perform actions depending onthe position on the page. A different page may have fixed data over theentire page so that no matter where the pen clicks on the page, the samedata will be returned. Another page may simply have giant tags over thepage as a form of watermark—the mere presence of the tag is enough. Thefixed data and variable data can be anything—as long as the readingapplication can extract the data from the read tag and then interpretthe data it is useful.

The structure of the tag is user-definable to enable differentapplications build appropriate structures to hold their data. Ideally atag has some structure to help the locating software (in the pen) detectit, and some orientation features to enable the data bits to beextracted correctly. Finally, the data embedded in the tag should beredundantly encoded to allow the reading equipment (the pen) to correcterrors due to dust, grime, dirt, reading noise etc.

The tag is defined in terms of 1600 dpi dots to enable nicely shaped tagstructures. However it is not useful at present to print data dots on toa page where each data dot is represented by a single printed dot. Theerror introduced in the reading environment would be too severe. Youwould need at least a 3200 dpi scanner in the pen to be able to get the1600 dpi dots back again. Consequently a tag designer will typicallycluster a number of physical printed dots on the page to represent asingle data dot. This cluster of printed dots is referred to as amacrodot since it represents a single logical dot, and is clusteredtogether to ease dot detection and decoding algorithms in the readingdevice. Since the Tag Format Structure allows any output dot within atag to come from any data bit the size and shape of a macrodot iscompletely arbitrary. The tag designer will design the macrodot basedupon the reading and optical capabilities of the pen.

A Tag Encoder should ideally be capable of printing tags in landscapeand portrait modes. A single Tag Format Structure that is internallyrotated by the Tag Encoder is one way of doing it, but in our TagEncoder we simply have the Tag Encoder read a pre-rotated Tag FormatStructure to save the bother of rotating it ourselves.

Finally, in terms of placement of tags on a page, placing tags in atriangular grid is better than on a rectangular grid in terms of inkusage. Triangular grids are also convenient when placing tags on anarbitrarily curved surface, although our particular tag encoder onlycopes with rectangular planes. Thus the same tag interactive pen canread tags printed on other surfaces.

The tag encoder typically requires the presence of IR ink at the printhead although other inks such as K might be used for tags in limitedcircumstances.

The tag encoder works to effect tag generation at speed, in step withwhatever other image planes are being worked. It achieves speed byworking with a predefined tag format into which fixed and variablecomponents of a tag are fed to generate tags dot by dot delivering themline by line to a compositor as image planes are composited. It canencode fixed data for the page being printed, together with specificvariable tag data values, into an error-correctable encoded tag which issubsequently printed, usually in infrared, or sometimes in black ink onthe page. The tag encoder ideally regularly locates tags on a page,ideally placing tags on a preferably triangular grid. Those skilled inthe art will recognise that other tag arrays beside triangular might beused. The tag encoder allows for both landscape and portraitorientations. Basic tag structures are rendered at 1600 dpi, while tagdata is encoded as arbitarliy shaped macrodots (with a minimum size of 1dot at 1600 dpi). The output dot stream might be created in an outputorder set to match a particular printer, although those skilled in theart will appreciate that other regimes might be evolved. Further, thoseskilled in the art will appreciate the advantages of use of infraredink, not visible to the eye but detectable by appropriate sensors, andwill realise that other inks may sometimes have a use.

Instead of sending data packages to the print engine/controller (PEC)already encoded, bandwidth to the PEC is reduced by having the PEC dothe redundancy encoding. Specifically described is use of Reed-Solomonencoding, but it could equally be any other encoder. The PEC preferablyencodes both the fixed and variable parts of the tag data.

The invention defines a template that gives a generic data package thatincludes dots that are always off, always on, and derived from theencoded data. This allows for development of any of a range of datapackage defintions, including macrodots of different sizes, largeobjects to help location, and so forth. Tag structures might be storedin associated DRAM where implementation does not involve fabrication ofan all embracing chip. A trivial extension is to have the tag structureon-chip instead of in the external DRAM.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and other embodiments of the invention will now be described,by way of non-limiting example only, with reference to the accompanyingdrawings, in which:

FIG. 1 is a schematic of a the relationship between a sample printednetpage and its online page description;

FIG. 2 is a schematic view of a interaction between a netpage pen, anetpage printer, a netpage page server, and a netpage applicationserver;

FIG. 3 illustrates a collection of netpage servers and printersinterconnected via a network;

FIG. 4 is a schematic view of a high-level structure of a printednetpage and its online page description;

FIG. 5 is a plan view showing a structure of a netpage tag;

FIG. 6 is a plan view showing a relationship between a set of the tagsshown in FIG. 5 and a field of view of a netpage sensing device in theform of a netpage pen;

FIG. 7 is a flowchart of a tag image processing and decoding algorithm;

FIG. 8 is a perspective view of a netpage pen and its associatedtag-sensing field-of-view cone;

FIG. 9 is a perspective exploded view of the netpage pen shown in FIG.8;

FIG. 10 is a schematic block diagram of a pen controller for the netpagepen shown in FIGS. 8 and 9;

FIG. 11 is a perspective view of a wall-mounted netpage printer;

FIG. 12 is a section through the length of the netpage printer of FIG.11;

FIG. 12A is an enlarged portion of FIG. 12 showing a section of theduplexed print engines and glue wheel assembly;

FIG. 13 is a detailed view of the ink cartridge, ink, air and gluepaths, and print engines of the netpage printer of FIGS. 11 and 12;

FIG. 14 is a schematic block diagram of a printer controller for thenetpage printer shown in FIGS. 11 and 12;

FIG. 15 is a schematic block diagram of duplexed print enginecontrollers and Memjet printheads associated with the printer controllershown in FIG. 14;

FIG. 16 is a schematic block diagram of the print engine controllershown in FIGS. 14 and 15;

FIG. 17 is a perspective view of a single Memjet printing element, asused in, for example, the netpage printer of FIGS. 10 to 12;

FIG. 18 is a perspective view of a small part of an array of Memjetprinting elements;

FIG. 19 is a series of perspective views illustrating the operatingcycle of the Memjet printing element shown in FIG. 13;

FIG. 20 is a perspective view of a short segment of a pagewidth Memjetprinthead;

FIG. 21 is a schematic view of a user class diagram;

FIG. 22 is a schematic view of a printer class diagram;

FIG. 23 is a schematic view of a pen class diagram;

FIG. 24 is a schematic view of an application class diagram;

FIG. 25 is a schematic view of a document and page description classdiagram;

FIG. 26 is a schematic view of a document and page ownership classdiagram;

FIG. 27 is a schematic view of a terminal element specialization classdiagram;

FIG. 28 is a schematic view of a static element specialization classdiagram;

FIG. 29 is a schematic view of a hyperlink element class diagram;

FIG. 30 is a schematic view of a hyperlink element specialization classdiagram;

FIG. 31 is a schematic view of a hyperlinked group class diagram;

FIG. 32 is a schematic view of a form class diagram;

FIG. 33 is a schematic view of a digital ink class diagram;

FIG. 34 is a schematic view of a field element specialization classdiagram;

FIG. 35 is a schematic view of a checkbox field class diagram;

FIG. 36 is a schematic view of a text field class diagram;

FIG. 37 is a schematic view of a signature field class diagram;

FIG. 38 is a flowchart of an input processing algorithm;

FIG. 38A is a detailed flowchart of one step of the flowchart of FIG.38;

FIG. 39 is a schematic view of a page server command element classdiagram;

FIG. 40 is a schematic view of a resource description class diagram;

FIG. 41 is a schematic view of a favorites list class diagram;

FIG. 42 is a schematic view of a history list class diagram;

FIG. 43 is a schematic view of a subscription delivery protocol;

FIG. 44 is a schematic view of a hyperlink request class diagram;

FIG. 45 is a schematic view of a hyperlink activation protocol;

FIG. 46 is a schematic view of a form submission protocol;

FIG. 47 is a schematic view of a commission payment protocol;

FIG. 48 is a diagram illustrating data flow and the functions performedby the print engine controller.

FIG. 49 shows the print engine controller in the context of the overallprinter system architecture.

FIG. 50 illustrates the print engine controller architecture.

FIG. 51 illustrates the external interfaces to the halftoner/compositorunit (HCU) of FIG. 50.

FIG. 52 is a diagram showing internal circuitry to the HCU of FIG. 51.

FIG. 53 shows a block diagram illustrating the process within the dotmerger unit of FIG. 52.

FIG. 54 shows a diagram illustrating the process within the dotreorganization unit of FIG. 52.

FIG. 55 illustrates a placement of tags in portrait and landscape modes.

FIG. 56 represents the parameters used to define tag placement.

FIG. 57 indicates a half line tag data buffer structure.

FIG. 58 shows a circuit by which to generate a single tag dot.

FIG. 59 shows a Reed-Solomon based circuit encoding tag data.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Note: Memjet™ is a trade mark of Silverbrook Research Pty Ltd,Australia.

In the preferred embodiment, the invention is configured to work withthe netpage networked computer system, a detailed overview of whichfollows. It will be appreciated that not every implementation willnecessarily embody all or even most of the specific details andextensions discussed below in relation to the basic system. However, thesystem is described in its most complete form to reduce the need forexternal reference when attempting to understand the context in whichthe preferred embodiments and aspects of the present invention operate.

In brief summary, the preferred form of the netpage system employs acomputer interface in the form of a mapped surface, that is, a physicalsurface which contains references to a map of the surface maintained ina computer system. The map references can be queried by an appropriatesensing device. Depending upon the specific implementation, the mapreferences may be encoded visibly or invisibly, and defined in such away that a local query on the mapped surface yields an unambiguous mapreference both within the map and among different maps. The computersystem can contain information about features on the mapped surface, andsuch information can be retrieved based on map references supplied by asensing device used with the mapped surface. The information thusretrieved can take the form of actions which are initiated by thecomputer system on behalf of the operator in response to the operator'sinteraction with the surface features.

In its preferred form, the netpage system relies on the production of,and human interaction with, netpages. These are pages of text, graphicsand images printed on ordinary paper, but which work like interactiveweb pages. Information is encoded on each page using ink which issubstantially invisible to the unaided human eye. The ink, however, andthereby the coded data, can be sensed by an optically imaging pen andtransmitted to the netpage system.

In the preferred form, active buttons and hyperlinks on each page can beclicked with the pen to request information from the network or tosignal preferences to a network server. In one embodiment, text writtenby hand on a netpage is automatically recognized and converted tocomputer text in the netpage system, allowing forms to be filled in. Inother embodiments, signatures recorded on a netpage are automaticallyverified, allowing e-commerce transactions to be securely authorized.

As illustrated in FIG. 1, a printed netpage 1 can represent ainteractive form which can be filled in by the user both physically, onthe printed page, and “electronically”, via communication between thepen and the netpage system. The example shows a “Request” formcontaining name and address fields and a submit button. The netpageconsists of graphic data 2 printed using visible ink, and coded data 3printed as a collection of tags 4 using invisible ink. The correspondingpage description 5, stored on the netpage network, describes theindividual elements of the netpage. In particular it describes the typeand spatial extent (zone) of each interactive element (i.e. text fieldor button in the example), to allow the netpage system to correctlyinterpret input via the netpage. The submit button 6, for example, has azone 7 which corresponds to the spatial extent of the correspondinggraphic 8.

As illustrated in FIG. 2, the netpage pen 101, a preferred form of whichis shown in FIGS. 8 and 9 and described in more detail below, works inconjunction with a netpage printer 601, an Internet-connected printingappliance for home, office or mobile use. The pen is wireless andcommunicates securely with the netpage printer via a short-range radiolink 9.

The netpage printer 601, a preferred form of which is shown in FIGS. 11to 13 and described in more detail below, is able to deliver,periodically or on demand, personalized newspapers, magazines, catalogs,brochures and other publications, all printed at high quality asinteractive netpages. Unlike a personal computer, the netpage printer isan appliance which can be, for example, wall-mounted adjacent to an areawhere the morning news is first consumed, such as in a user's kitchen,near a breakfast table, or near the household's point of departure forthe day. It also comes in tabletop, desktop, portable and miniatureversions.

Netpages printed at their point of consumption combine the ease-of-useof paper with the timeliness and interactivity of an interactive medium.

As shown in FIG. 2, the netpage pen 101 interacts with the coded data ona printed netpage 1 and communicates, via a short-range radio link 9,the interaction to a netpage printer. The printer 601 sends theinteraction to the relevant netpage page server 10 for interpretation.In appropriate circumstances, the page server sends a correspondingmessage to application computer software running on a netpageapplication server 13. The application server may in turn send aresponse which is printed on the originating printer.

The netpage system is made considerably more convenient in the preferredembodiment by being used in conjunction with high-speedmicroelectromechanical system (MEMS) based inkjet (Memjet™) printers. Inthe preferred form of this technology, relatively high-speed andhigh-quality printing is made more affordable to consumers. In itspreferred form, a netpage publication has the physical characteristicsof a traditional newsmagazine, such as a set of letter-size glossy pagesprinted in full color on both sides, bound together for easy navigationand comfortable handling.

The netpage printer exploits the growing availability of broadbandInternet access. Cable service is available to 95% of households in theUnited States, and cable modem service offering broadband Internetaccess is already available to 20% of these. The netpage printer canalso operate with slower connections, but with longer delivery times andlower image quality. Indeed, the netpage system can be enabled usingexisting consumer inkjet and laser printers, although the system willoperate more slowly and will therefore be less acceptable from aconsumer's point of view. In other embodiments, the netpage system ishosted on a private intranet. In still other embodiments, the netpagesystem is hosted on a single computer or computer-enabled device, suchas a printer.

Netpage publication servers 14 on the netpage network are configured todeliver print-quality publications to netpage printers. Periodicalpublications are delivered automatically to subscribing netpage printersvia pointcasting and multicasting Internet protocols. Personalizedpublications are filtered and formatted according to individual userprofiles.

A netpage printer can be configured to support any number of pens, and apen can work with any number of netpage printers. In the preferredimplementation, each netpage pen has a unique identifier. A householdmay have a collection of colored netpage pens, one assigned to eachmember of the family. This allows each user to maintain a distinctprofile with respect to a netpage publication server or applicationserver.

A netpage pen can also be registered with a netpage registration server11 and linked to one or more payment card accounts. This allowse-commerce payments to be securely authorized using the netpage pen. Thenetpage registration server compares the signature captured by thenetpage pen with a previously registered signature, allowing it toauthenticate the user's identity to an e-commerce server. Otherbiometrics can also be used to verify identity. A version of the netpagepen includes fingerprint scanning, verified in a similar way by thenetpage registration server.

Although a netpage printer may deliver periodicals such as the morningnewspaper without user intervention, it can be configured never todeliver unsolicited junk mail. In its preferred form, it only deliversperiodicals from subscribed or otherwise authorized sources. In thisrespect, the netpage printer is unlike a fax machine or e-mail accountwhich is visible to any junk mailer who knows the telephone number oremail address.

1 Netpage System Architecture

Each object model in the system is described using a Unified ModelingLanguage (UML) class diagram. A class diagram consists of a set ofobject classes connected by relationships, and two kinds ofrelationships are of interest here: associations and generalizations. Anassociation represents some kind of relationship between objects, i.e.between instances of classes. A generalization relates actual classes,and can be understood in the following way: if a class is thought of asthe set of all objects of that class, and class A is a generalization ofclass B, then B is simply a subset of A. The UML does not directlysupport second-order modelling—i.e. classes of classes.

Each class is drawn as a rectangle labelled with the name of the class.It contains a list of the attributes of the class, separated from thename by a horizontal line, and a list of the operations of the class,separated from the attribute list by a horizontal line. In the classdiagrams which follow, however, operations are never modelled.

An association is drawn as a line joining two classes, optionallylabelled at either end with the multiplicity of the association. Thedefault multiplicity is one. An asterisk (*) indicates a multiplicity of“many”, i.e. zero or more. Each association is optionally labelled withits name, and is also optionally labelled at either end with the role ofthe corresponding class. An open diamond indicates an aggregationassociation (“is-part-of”), and is drawn at the aggregator end of theassociation line.

A generalization relationship (“is-a”) is drawn as a solid line joiningtwo classes, with an arrow (in the form of an open triangle) at thegeneralization end.

When a class diagram is broken up into multiple diagrams, any classwhich is duplicated is shown with a dashed outline in all but the maindiagram which defines it. It is shown with attributes only where it isdefined.

1.1 Netpages

Netpages are the foundation on which a netpage network is built. Theyprovide a paper-based user interface to published information andinteractive services.

A netpage consists of a printed page (or other surface region) invisiblytagged with references to an online description of the page. The onlinepage description is maintained persistently by a netpage page server.The page description describes the visible layout and content of thepage, including text, graphics and images. It also describes the inputelements on the page, including buttons, hyperlinks, and input fields. Anetpage allows markings made with a netpage pen on its surface to besimultaneously captured and processed by the netpage system.

Multiple netpages can share the same page description. However, to allowinput through otherwise identical pages to be distinguished, eachnetpage is assigned a unique page identifier. This page ID hassufficient precision to distinguish between a very large number ofnetpages.

Each reference to the page description is encoded in a printed tag. Thetag identifies the unique page on which it appears, and therebyindirectly identifies the page description. The tag also identifies itsown position on the page. Characteristics of the tags are described inmore detail below.

Tags are printed in infrared-absorptive ink on any substrate which isinfrared-reflective, such as ordinary paper. Near-infrared wavelengthsare invisible to the human eye but are easily sensed by a solid-stateimage sensor with an appropriate filter.

A tag is sensed by an area image sensor in the netpage pen, and the tagdata is transmitted to the netpage system via the nearest netpageprinter. The pen is wireless and communicates with the netpage printervia a short-range radio link. Tags are sufficiently small and denselyarranged that the pen can reliably image at least one tag even on asingle click on the page. It is important that the pen recognize thepage ID and position on every interaction with the page, since theinteraction is stateless. Tags are error-correctably encoded to makethem partially tolerant to surface damage.

The netpage page server maintains a unique page instance for eachprinted netpage, allowing it to maintain a distinct set of user-suppliedvalues for input fields in the page description for each printednetpage.

The relationship between the page description, the page instance, andthe printed netpage is shown in FIG. 4. The page instance is associatedwith both the netpage printer which printed it and, if known, thenetpage user who requested it.

1.2 Netpage Tags

1.2.1 Tag Data Content

In a preferred form, each tag identifies the region in which it appears,and the location of that tag within the region. A tag may also containflags which relate to the region as a whole or to the tag. One or moreflag bits may, for example, signal a tag sensing device to providefeedback indicative of a function associated with the immediate area ofthe tag, without the sensing device having to refer to a description ofthe region. A netpage pen may, for example, illuminate an “active area”LED when in the zone of a hyperlink.

As will be more clearly explained below, in a preferred embodiment, eachtag contains an easily recognized invariant structure which aids initialdetection, and which assists in minimizing the effect of any warpinduced by the surface or by the sensing process. The tags preferablytile the entire page, and are sufficiently small and densely arrangedthat the pen can reliably image at least one tag even on a single clickon the page. It is important that the pen recognize the page ID andposition on every interaction with the page, since the interaction isstateless.

In a preferred embodiment, the region to which a tag refers coincideswith an entire page, and the region ID encoded in the tag is thereforesynonymous with the page ID of the page on which the tag appears. Inother embodiments, the region to which a tag refers can be an arbitrarysubregion of a page or other surface. For example, it can coincide withthe zone of an interactive element, in which case the region ID candirectly identify the interactive element.

TABLE 1 Tag data Field Precision (bits) Region ID 100 Tag ID 16 Flags 4Total 120

Each tag contains 120 bits of information, typically allocated as shownin Table 1. Assuming a maximum tag density of 64 per square inch, a16-bit tag ID supports a region size of up to 1024 square inches. Largerregions can be mapped continuously without increasing the tag IDprecision simply by using abutting regions and maps. The 100-bit regionID allows 2¹⁰⁰ (˜10³° or a million trillion trillion) different regionsto be uniquely identified.

1.2.2 Tag Data Encoding

The 120 bits of tag data are redundantly encoded using a (15, 5)Reed-Solomon code. This yields 360 encoded bits consisting of 6codewords of 15 4-bit symbols each. The (15, 5) code allows up to 5symbol errors to be corrected per codeword, i.e. it is tolerant of asymbol error rate of up to 33% per codeword.

Each 4-bit symbol is represented in a spatially coherent way in the tag,and the symbols of the six codewords are interleaved spatially withinthe tag. This ensures that a burst error (an error affecting multiplespatially adjacent bits) damages a minimum number of symbols overall anda minimum number of symbols in any one codeword, thus maximising thelikelihood that the burst error can be fully corrected.

1.2.3 Physical Tag Structure

The physical representation of the tag, shown in FIG. 5, includes fixedtarget structures 15, 16, 17 and variable data areas 18. The fixedtarget structures allow a sensing device such as the netpage pen todetect the tag and infer its three-dimensional orientation relative tothe sensor. The data areas contain representations of the individualbits of the encoded tag data. To achieve proper tag reproduction, thetag is rendered at a resolution of 256×256 dots.

When printed at 1600 dots per inch this yields a tag with a diameter ofabout 4 mm. At this resolution the tag is designed to be surrounded by a“quiet area” of radius 16 dots. Since the quiet area is also contributedby adjacent tags, it only adds 16 dots to the effective diameter of thetag.

The tag includes six target structures. A detection ring 15 allows thesensing device to initially detect the tag. The ring is easy to detectbecause it is rotationally invariant and because a simple correction ofits aspect ratio removes most of the effects of perspective distortion.An orientation axis 16 allows the sensing device to determine theapproximate planar orientation of the tag due to the yaw of the sensor.The orientation axis is skewed to yield a unique orientation. Fourperspective targets 17 allow the sensing device to infer an accuratetwo-dimensional perspective transform of the tag and hence an accuratethree-dimensional position and orientation of the tag relative to thesensor.

All target structures are redundantly large to improve their immunity tonoise.

The overall tag shape is circular. This supports, amongst other things,optimal tag packing on an irregular triangular grid. In combination withthe circular detection ring, this makes a circular arrangement of databits within the tag optimal. To maximise its size, each data bit isrepresented by a radial wedge in the form of an area bounded by tworadial lines and two concentric circular arcs. Each wedge has a minimumdimension of 8 dots at 1600 dpi and is designed so that its base (itsinner arc), is at least equal to this minimum dimension. The height ofthe wedge in the radial direction is always equal to the minimumdimension. Each 4-bit data symbol is represented by an array of 2×2wedges.

The 15 4-bit data symbols of each of the six codewords are allocated tothe four concentric symbol rings 18 a to 18 d in interleaved fashion.Symbols are allocated alternately in circular progression around thetag.

The interleaving is designed to maximise the average spatial distancebetween any two symbols of the same codeword.

In order to support “single-click” interaction with a tagged region viaa sensing device, the sensing device must be able to see at least oneentire tag in its field of view no matter where in the region or at whatorientation it is positioned. The required diameter of the field of viewof the sensing device is therefore a function of the size and spacing ofthe tags.

Assuming a circular tag shape, the minimum diameter of the sensor fieldof view is obtained when the tags are tiled on a equilateral triangulargrid, as shown in FIG. 6.

1.2.5 Tag Image Processing and Decoding

The tag image processing and decoding performed by a sensing device suchas the netpage pen is shown in FIG. 7. While a captured image is beingacquired from the image sensor, the dynamic range of the image isdetermined (at 20). The center of the range is then chosen as the binarythreshold for the image 21. The image is then thresholded and segmentedinto connected pixel regions (i.e. shapes 23) (at 22). Shapes which aretoo small to represent tag target structures are discarded. The size andcentroid of each shape is also computed.

Binary shape moments 25 are then computed (at 24) for each shape, andthese provide the basis for subsequently locating target structures.Central shape moments are by their nature invariant of position, and canbe easily made invariant of scale, aspect ratio and rotation.

The ring target structure 15 is the first to be located (at 26). A ringhas the advantage of being very well behaved when perspective-distorted.Matching proceeds by aspect-normalizing and rotation-normalizing eachshape's moments. Once its second-order moments are normalized the ringis easy to recognize even if the perspective distortion was significant.The ring's original aspect and rotation 27 together provide a usefulapproximation of the perspective transform.

The axis target structure 16 is the next to be located (at 28). Matchingproceeds by applying the ring's normalizations to each shape's moments,and rotation-normalizing the resulting moments. Once its second-ordermoments are normalized the axis target is easily recognized. Note thatone third order moment is required to disambiguate the two possibleorientations of the axis. The shape is deliberately skewed to one sideto make this possible. Note also that it is only possible torotation-normalize the axis target after it has had the ring'snormalizations applied, since the perspective distortion can hide theaxis target's axis. The axis target's original rotation provides auseful approximation of the tag's rotation due to pen yaw 29.

The four perspective target structures 17 are the last to be located (at30). Good estimates of their positions are computed based on their knownspatial relationships to the ring and axis targets, the aspect androtation of the ring, and the rotation of the axis. Matching proceeds byapplying the ring's normalizations to each shape's moments. Once theirsecond-order moments are normalized the circular perspective targets areeasy to recognize, and the target closest to each estimated position istaken as a match. The original centroids of the four perspective targetsare then taken to be the perspective-distorted corners 31 of a square ofknown size in tag space, and an eight-degree-of-freedom perspectivetransform 33 is inferred (at 32) based on solving the well-understoodequations relating the four tag-space and image-space point pairs.

The inferred tag-space to image-space perspective transform is used toproject (at 36) each known data bit position in tag space into imagespace where the real-valued position is used to bilinearly interpolate(at 36) the four relevant adjacent pixels in the input image. Thepreviously computed image threshold 21 is used to threshold the resultto produce the final bit value 37.

Once all 360 data bits 37 have been obtained in this way, each of thesix 60-bit Reed-Solomon codewords is decoded (at 38) to yield 20 decodedbits 39, or 120 decoded bits in total. Note that the codeword symbolsare sampled in codeword order, so that codewords are implicitlyde-interleaved during the sampling process.

The ring target 15 is only sought in a subarea of the image whoserelationship to the image guarantees that the ring, if found, is part ofa complete tag. If a complete tag is not found and successfully decoded,then no pen position is recorded for the current frame. Given adequateprocessing power and ideally a non-minimal field of view 193, analternative strategy involves seeking another tag in the current image.

The obtained tag data indicates the identity of the region containingthe tag and the position of the tag within the region. An accurateposition 35 of the pen nib in the region, as well as the overallorientation 35 of the pen, is then inferred (at 34) from the perspectivetransform 33 observed on the tag and the known spatial relationshipbetween the pen's physical axis and the pen's optical axis.

1.2.6 Tag Map

Decoding a tag results in a region ID, a tag ID, and a tag-relative pentransform. Before the tag ID and the tag-relative pen location can betranslated into an absolute location within the tagged region, thelocation of the tag within the region must be known. This is given by atag map, a function which maps each tag ID in a tagged region to acorresponding location. The tag map class diagram is shown in FIG. 22,as part of the netpage printer class diagram.

A tag map reflects the scheme used to tile the surface region with tags,and this can vary according to surface type. When multiple taggedregions share the same tiling scheme and the same tag numbering scheme,they can also share the same tag map.

The tag map for a region must be retrievable via the region ID. Thus,given a region ID, a tag ID and a pen transform, the tag map can beretrieved, the tag ID can be translated into an absolute tag locationwithin the region, and the tag-relative pen location can be added to thetag location to yield an absolute pen location within the region.

1.2.7 Tagging Schemes

Two distinct surface coding schemes are of interest, both of which usethe tag structure described earlier in this section. The preferredcoding scheme uses “location-indicating” tags as already discussed. Analternative coding scheme uses object-indicating tags.

A location-indicating tag contains a tag ID which, when translatedthrough the tag map associated with the tagged region, yields a uniquetag location within the region. The tag-relative location of the pen isadded to this tag location to yield the location of the pen within theregion. This in turn is used to determine the location of the penrelative to a user interface element in the page description associatedwith the region. Not only is the user interface element itselfidentified, but a location relative to the user interface element isidentified. Location-indicating tags therefore trivially support thecapture of an absolute pen path in the zone of a particular userinterface element.

An object-indicating tag contains a tag ID which directly identifies auser interface element in the page description associated with theregion. All the tags in the zone of the user interface element identifythe user interface element, making them all identical and thereforeindistinguishable. Object-indicating tags do not, therefore, support thecapture of an absolute pen path. They do, however, support the captureof a relative pen path. So long as the position sampling frequencyexceeds twice the encountered tag frequency, the displacement from onesampled pen position to the next within a stroke can be unambiguouslydetermined.

With either tagging scheme, the tags function in cooperation withassociated visual elements on the netpage as user interactive elementsin that a user can interact with the printed page using an appropriatesensing device in order for tag data to be read by the sensing deviceand for an appropriate response to be generated in the netpage system.

1.3 Document and Page Descriptions

A preferred embodiment of a document and page description class diagramis shown in FIGS. 25 and 26.

In the netpage system a document is described at three levels. At themost abstract level the document 836 has a hierarchical structure whoseterminal elements 839 are associated with content objects 840 such astext objects, text style objects, image objects, etc. Once the documentis printed on a printer with a particular page size and according to aparticular user's scale factor preference, the document is paginated andotherwise formatted. Formatted terminal elements 835 will in some casesbe associated with content objects which are different from thoseassociated with their corresponding terminal elements, particularlywhere the content objects are style-related. Each printed instance of adocument and page is also described separately, to allow input capturedthrough a particular page instance 830 to be recorded separately frominput captured through other instances of the same page description.

The presence of the most abstract document description on the pageserver allows a user to request a copy of a document without beingforced to accept the source document's specific format. The user may berequesting a copy through a printer with a different page size, forexample. Conversely, the presence of the formatted document descriptionon the page server allows the page server to efficiently interpret useractions on a particular printed page.

A formatted document 834 consists of a set of formatted pagedescriptions 5, each of which consists of a set of formatted terminalelements 835. Each formatted element has a spatial extent or zone 58 onthe page. This defines the active area of input elements such ashyperlinks and input fields.

A document instance 831 corresponds to a formatted document 834. Itconsists of a set of page instances 830, each of which corresponds to apage description 5 of the formatted document. Each page instance 830describes a single unique printed netpage 1, and records the page ID 50of the netpage. A page instance is not part of a document instance if itrepresents a copy of a page requested in isolation.

A page instance consists of a set of terminal element instances 832. Anelement instance only exists if it records instance-specificinformation. Thus, a hyperlink instance exists for a hyperlink elementbecause it records a transaction ID 55 which is specific to the pageinstance, and a field instance exists for a field element because itrecords input specific to the page instance. An element instance doesnot exist, however, for static elements such as textflows.

A terminal element can be a static element 843, a hyperlink element 844,a field element 845 or a page server command element 846, as shown inFIG. 27. A static element 843 can be a style element 847 with anassociated style object 854, a textflow element 848 with an associatedstyled text object 855, an image element 849 with an associated imageelement 856, a graphic element 850 with an associated graphic object857, a video clip element 851 with an associated video clip object 858,an audio clip element 852 with an associated audio clip object 859, or ascript element 853 with an associated script object 860, as shown inFIG. 28.

A page instance has a background field 833 which is used to record anydigital ink captured on the page which does not apply to a specificinput element.

In the preferred form of the invention, a tag map 811 is associated witheach page instance to allow tags on the page to be translated intolocations on the page.

1.4 The Netpage Network

In a preferred embodiment, a netpage network consists of a distributedset of netpage page servers 10, netpage registration servers 11, netpageID servers 12, netpage application servers 13, netpage publicationservers 14, and netpage printers 601 connected via a network 19 such asthe Internet, as shown in FIG. 3.

The netpage registration server 11 is a server which recordsrelationships between users, pens, printers, applications andpublications, and thereby authorizes various network activities. Itauthenticates users and acts as a signing proxy on behalf ofauthenticated users in application transactions. It also provideshandwriting recognition services. As described above, a netpage pageserver 10 maintains persistent information about page descriptions andpage instances. The netpage network includes any number of page servers,each handling a subset of page instances. Since a page server alsomaintains user input values for each page instance, clients such asnetpage printers send netpage input directly to the appropriate pageserver. The page server interprets any such input relative to thedescription of the corresponding page.

A netpage ID server 12 allocates document IDs 51 on demand, and providesload-balancing of page servers via its ID allocation scheme.

A netpage printer uses the Internet Distributed Name System (DNS), orsimilar, to resolve a netpage page ID 50 into the network address of thenetpage page server handling the corresponding page instance.

A netpage application server 13 is a server which hosts interactivenetpage applications. A netpage publication server 14 is an applicationserver which publishes netpage documents to netpage printers. They aredescribed in detail in Section 2.

Netpage servers can be hosted on a variety of network server platformsfrom manufacturers such as IBM, Hewlett-Packard, and Sun. Multiplenetpage servers can run concurrently on a single host, and a singleserver can be distributed over a number of hosts. Some or all of thefunctionality provided by netpage servers, and in particular thefunctionality provided by the ID server and the page server, can also beprovided directly in a netpage appliance such as a netpage printer, in acomputer workstation, or on a local network.

1.5 The Netpage Printer

The netpage printer 601 is an appliance which is registered with thenetpage system and prints netpage documents on demand and viasubscription. Each printer has a unique printer ID 62, and is connectedto the netpage network via a network such as the Internet, ideally via abroadband connection.

Apart from identity and security settings in non-volatile memory, thenetpage printer contains no persistent storage. As far as a user isconcerned, “the network is the computer”. Netpages functioninteractively across space and time with the help of the distributednetpage page servers 10, independently of particular netpage printers.

The netpage printer receives subscribed netpage documents from netpagepublication servers 14. Each document is distributed in two parts: thepage layouts, and the actual text and image objects which populate thepages. Because of personalization, page layouts are typically specificto a particular subscriber and so are pointcast to the subscriber'sprinter via the appropriate page server. Text and image objects, on theother hand, are typically shared with other subscribers, and so aremulticast to all subscribers' printers and the appropriate page servers.

The netpage publication server optimizes the segmentation of documentcontent into pointcasts and multicasts. After receiving the pointcast ofa document's page layouts, the printer knows which multicasts, if any,to listen to.

Once the printer has received the complete page layouts and objects thatdefine the document to be printed, it can print the document.

The printer rasterizes and prints odd and even pages simultaneously onboth sides of the sheet. It contains duplexed print engine controllers760 and print engines utilizing Memjet™ printheads 350 for this purpose.

The printing process consists of two decoupled stages: rasterization ofpage descriptions, and expansion and printing of page images. The rasterimage processor (RIP) consists of one or more standard DSPs 757 runningin parallel. The duplexed print engine controllers consist of customprocessors which expand, dither and print page images in real time,synchronized with the operation of the printheads in the print engines.

Printers not enabled for IR printing have the option to print tags usingIR-absorptive black ink, although this restricts tags to otherwise emptyareas of the page. Although such pages have more limited functionalitythan IR-printed pages, they are still classed as netpages.

A normal netpage printer prints netpages on sheets of paper. Morespecialised netpage printers may print onto more specialised surfaces,such as globes. Each printer supports at least one surface type, andsupports at least one tag tiling scheme, and hence tag map, for eachsurface type. The tag map 811 which describes the tag tiling schemeactually used to print a document becomes associated with that documentso that the document's tags can be correctly interpreted.

FIG. 2 shows the netpage printer class diagram, reflectingprinter-related information maintained by a registration server 11 onthe netpage network.

A preferred embodiment of the netpage printer is described in greaterdetail in Section 6 below, with reference to FIGS. 11 to 16.

1.5.1 Memjet™ Printheads

The netpage system can operate using printers made with a wide range ofdigital printing technologies, including thermal inkjet, piezoelectricinkjet, laser electrophotographic, and others. However, for wideconsumer acceptance, it is desirable that a netpage printer have thefollowing characteristics:

-   -   photographic quality color printing    -   high quality text printing    -   high reliability    -   low printer cost    -   low ink cost    -   low paper cost    -   simple operation    -   nearly silent printing    -   high printing speed    -   simultaneous double sided printing    -   compact form factor    -   low power consumption

No commercially available printing technology has all of thesecharacteristics.

To enable to production of printers with these characteristics, thepresent applicant has invented a new print technology, referred to asMemjet™ technology. Memjet™ is a drop-on-demand inkjet technology thatincorporates pagewidth printheads fabricated usingmicroelectromechanical systems (MEMS) technology. FIG. 17 shows a singleprinting element 300 of a Memjet™ printhead. The netpage wallprinterincorporates 168960 printing elements 300 to form a 1600 dpi pagewidthduplex printer. This printer simultaneously prints cyan, magenta,yellow, black, and infrared inks as well as paper conditioner and inkfixative.

The printing element 300 is approximately 110 microns long by 32 micronswide. Arrays of these printing elements are formed on a siliconsubstrate 301 that incorporates CMOS logic, data transfer, timing, anddrive circuits (not shown).

Major elements of the printing element 300 are the nozzle 302, thenozzle rim 303, the nozzle chamber 304, the fluidic seal 305, the inkchannel rim 306, the lever arm 307, the active actuator beam pair 308,the passive actuator beam pair 309, the active actuator anchor 310, thepassive actuator anchor 311, and the ink inlet 312.

The active actuator beam pair 308 is mechanically joined to the passiveactuator beam pair 309 at the join 319. Both beams pairs are anchored attheir respective anchor points 310 and 311. The combination of elements308, 309, 310, 311, and 319 form a cantilevered electrothermal bendactuator 320.

FIG. 18 shows a small part of an array of printing elements 300,including a cross section 315 of a printing element 300. The crosssection 315 is shown without ink, to clearly show the ink inlet 312 thatpasses through the silicon wafer 301.

FIGS. 19( a), 19(b) and 19(c) show the operating cycle of a Memjet™printing element 300.

FIG. 19( a) shows the quiescent position of the ink meniscus 316 priorto printing an ink droplet Ink is retained in the nozzle chamber bysurface tension at the ink meniscus 316 and at the fluidic seal 305formed between the nozzle chamber 304 and the ink channel rim 306.

While printing, the printhead CMOS circuitry distributes data from theprint engine controller to the correct printing element, latches thedata, and buffers the data to drive the electrodes 318 of the activeactuator beam pair 308. This causes an electrical current to passthrough the beam pair 308 for about one microsecond, resulting in Jouleheating. The temperature increase resulting from Joule heating causesthe beam pair 308 to expand. As the passive actuator beam pair 309 isnot heated, it does not expand, resulting in a stress difference betweenthe two beam pairs. This stress difference is partially resolved by thecantilevered end of the electrothermal bend actuator 320 bending towardsthe substrate 301. The lever arm 307 transmits this movement to thenozzle chamber 304. The nozzle chamber 304 moves about two microns tothe position shown in FIG. 19( b). This increases the ink pressure,forcing ink 321 out of the nozzle 302, and causing the ink meniscus 316to bulge. The nozzle rim 303 prevents the ink meniscus 316 fromspreading across the surface of the nozzle chamber 304.

As the temperature of the beam pairs 308 and 309 equalizes, the actuator320 returns to its original position. This aids in the break-off of theink droplet 317 from the ink 321 in the nozzle chamber, as shown in FIG.19( c). The nozzle chamber is refilled by the action of the surfacetension at the meniscus 316.

FIG. 20 shows a segment of a printhead 350. In a netpage printer, thelength of the printhead is the full width of the paper (typically 210mm) in the direction 351. The segment shown is 0.4 mm long (about 0.2%of a complete printhead). When printing, the paper is moved past thefixed printhead in the direction 352. The printhead has 6 rows ofinterdigitated printing elements 300, printing the six colors or typesof ink supplied by the ink inlets 312.

To protect the fragile surface of the printhead during operation, anozzle guard wafer 330 is attached to the printhead substrate 301. Foreach nozzle 302 there is a corresponding nozzle guard hole 331 throughwhich the ink droplets are fired. To prevent the nozzle guard holes 331from becoming blocked by paper fibers or other debris, filtered air ispumped through the air inlets 332 and out of the nozzle guard holesduring printing. To prevent ink 321 from drying, the nozzle guard issealed while the printer is idle.

1.6 The Netpage Pen

The active sensing device of the netpage system is typically a pen 101,which, using its embedded controller 134, is able to capture and decodeIR position tags from a page via an image sensor. The image sensor is asolid-state device provided with an appropriate filter to permit sensingat only near-infrared wavelengths. As described in more detail below,the system is able to sense when the nib is in contact with the surface,and the pen is able to sense tags at a sufficient rate to capture humanhandwriting (i.e. at 200 dpi or greater and 100 Hz or faster).Information captured by the pen is encrypted and wirelessly transmittedto the printer (or base station), the printer or base stationinterpreting the data with respect to the (known) page structure.

The preferred embodiment of the netpage pen operates both as a normalmarking ink pen and as a non-marking stylus. The marking aspect,however, is not necessary for using the netpage system as a browsingsystem, such as when it is used as an Internet interface. Each netpagepen is registered with the netpage system and has a unique pen ID 61.FIG. 23 shows the netpage pen class diagram, reflecting pen-relatedinformation maintained by a registration server 11 on the netpagenetwork.

When either nib is in contact with a netpage, the pen determines itsposition and orientation relative to the page. The nib is attached to aforce sensor, and the force on the nib is interpreted relative to athreshold to indicate whether the pen is “up” or “down”. This allows ainteractive element on the page to be ‘clicked’ by pressing with the pennib, in order to request, say, information from a network. Furthermore,the force is captured as a continuous value to allow, say, the fulldynamics of a signature to be verified.

The pen determines the position and orientation of its nib on thenetpage by imaging, in the infrared spectrum, an area 193 of the page inthe vicinity of the nib. It decodes the nearest tag and computes theposition of the nib relative to the tag from the observed perspectivedistortion on the imaged tag and the known geometry of the pen optics.Although the position resolution of the tag may be low, because the tagdensity on the page is inversely proportional to the tag size, theadjusted position resolution is quite high, exceeding the minimumresolution required for accurate handwriting recognition.

Pen actions relative to a netpage are captured as a series of strokes. Astroke consists of a sequence of time-stamped pen positions on the page,initiated by a pen-down event and completed by the subsequent pen-upevent. A stroke is also tagged with the page ID 50 of the netpagewhenever the page ID changes, which, under normal circumstances, is atthe commencement of the stroke.

Each netpage pen has a current selection 826 associated with it,allowing the user to perform copy and paste operations etc. Theselection is timestamped to allow the system to discard it after adefined time period. The current selection describes a region of a pageinstance. It consists of the most recent digital ink stroke capturedthrough the pen relative to the background area of the page. It isinterpreted in an application-specific manner once it is submitted to anapplication via a selection hyperlink activation.

Each pen has a current nib 824. This is the nib last notified by the pento the system. In the case of the default netpage pen described above,either the marking black ink nib or the non-marking stylus nib iscurrent. Each pen also has a current nib style 825. This is the nibstyle last associated with the pen by an application, e.g. in responseto the user selecting a color from a palette. The default nib style isthe nib style associated with the current nib. Strokes captured througha pen are tagged with the current nib style. When the strokes aresubsequently reproduced, they are reproduced in the nib style with whichthey are tagged.

Whenever the pen is within range of a printer with which it cancommunicate, the pen slowly flashes its “online” LED. When the pen failsto decode a stroke relative to the page, it momentarily activates its“error” LED. When the pen succeeds in decoding a stroke relative to thepage, it momentarily activates its “ok” LED.

A sequence of captured strokes is referred to as digital ink. Digitalink forms the basis for the digital exchange of drawings andhandwriting, for online recognition of handwriting, and for onlineverification of signatures.

The pen is wireless and transmits digital ink to the netpage printer viaa short-range radio link. The transmitted digital ink is encrypted forprivacy and security and packetized for efficient transmission, but isalways flushed on a pen-up event to ensure timely handling in theprinter.

When the pen is out-of-range of a printer it buffers digital ink ininternal memory, which has a capacity of over ten minutes of continuoushandwriting. When the pen is once again within range of a printer, ittransfers any buffered digital ink.

A pen can be registered with any number of printers, but because allstate data resides in netpages both on paper and on the network, it islargely immaterial which printer a pen is communicating with at anyparticular time.

A preferred embodiment of the pen is described in greater detail inSection 6 below, with reference to FIGS. 8 to 10.

1.7 Netpage Interaction

The netpage printer 601 receives data relating to a stroke from the pen101 when the pen is used to interact with a netpage 1. The coded data 3of the tags 4 is read by the pen when it is used to execute a movement,such as a stroke. The data allows the identity of the particular pageand associated interactive element to be determined and an indication ofthe relative positioning of the pen relative to the page to be obtained.The indicating data is transmitted to the printer, where it resolves,via the DNS, the page ID 50 of the stroke into the network address ofthe netpage page server 10 which maintains the corresponding pageinstance 830. It then transmits the stroke to the page server. If thepage was recently identified in an earlier stroke, then the printer mayalready have the address of the relevant page server in its cache. Eachnetpage consists of a compact page layout maintained persistently by anetpage page server (see below). The page layout refers to objects suchas images, fonts and pieces of text, typically stored elsewhere on thenetpage network.

When the page server receives the stroke from the pen, it retrieves thepage description to which the stroke applies, and determines whichelement of the page description the stroke intersects. It is then ableto interpret the stroke in the context of the type of the relevantelement.

A “click” is a stroke where the distance and time between the pen downposition and the subsequent pen up position are both less than somesmall maximum. An object which is activated by a click typicallyrequires a click to be activated, and accordingly, a longer stroke isignored. The failure of a pen action, such as a “sloppy” click, toregister is indicated by the lack of response from the pen's “ok” LED.

There are two kinds of input elements in a netpage page description:hyperlinks and form fields. Input through a form field can also triggerthe activation of an associated hyperlink.

1.7.1 Hyperlinks

A hyperlink is a means of sending a message to a remote application, andtypically elicits a printed response in the netpage system.

A hyperlink element 844 identifies the application 71 which handlesactivation of the hyperlink, a link ID 54 which identifies the hyperlinkto the application, an “alias required” flag which asks the system toinclude the user's application alias ID 65 in the hyperlink activation,and a description which is used when the hyperlink is recorded as afavorite or appears in the user's history. The hyperlink element classdiagram is shown in FIG. 29.

When a hyperlink is activated, the page server sends a request to anapplication somewhere on the network. The application is identified byan application ID 64, and the application ID is resolved in the normalway via the DNS. There are three types of hyperlinks: general hyperlinks863, form hyperlinks 865, and selection hyperlinks 864, as shown in FIG.30. A general hyperlink can implement a request for a linked document,or may simply signal a preference to a server. A form hyperlink submitsthe corresponding form to the application. A selection hyperlink submitsthe current selection to the application. If the current selectioncontains a single-word piece of text, for example, the application mayreturn a single-page document giving the word's meaning within thecontext in which it appears, or a translation into a different language.Each hyperlink type is characterized by what information is submitted tothe application.

The corresponding hyperlink instance 862 records a transaction ID 55which can be specific to the page instance on which the hyperlinkinstance appears. The transaction ID can identify user-specific data tothe application, for example a “shopping cart” of pending purchasesmaintained by a purchasing application on behalf of the user.

The system includes the pen's current selection 826 in a selectionhyperlink activation. The system includes the content of the associatedform instance 868 in a form hyperlink activation, although if thehyperlink has its “submit delta” attribute set, only input since thelast form submission is included. The system includes an effectivereturn path in all hyperlink activations.

A hyperlinked group 866 is a group element 838 which has an associatedhyperlink, as shown in FIG. 31. When input occurs through any fieldelement in the group, the hyperlink 844 associated with the group isactivated. A hyperlinked group can be used to associate hyperlinkbehavior with a field such as a checkbox. It can also be used, inconjunction with the “submit delta” attribute of a form hyperlink, toprovide continuous input to an application. It can therefore be used tosupport a “blackboard” interaction model, i.e. where input is capturedand therefore shared as soon as it occurs.

1.7.2 Forms

A form defines a collection of related input fields used to capture arelated set of inputs through a printed netpage. A form allows a user tosubmit one or more parameters to an application software program runningon a server.

A form 867 is a group element 838 in the document hierarchy. Itultimately contains a set of terminal field elements 839. A forminstance 868 represents a printed instance of a form. It consists of aset of field instances 870 which correspond to the field elements 845 ofthe form. Each field instance has an associated value 871, whose typedepends on the type of the corresponding field element. Each field valuerecords input through a particular printed form instance, i.e. throughone or more printed netpages. The form class diagram is shown in FIG.32.

Each form instance has a status 872 which indicates whether the form isactive, frozen, submitted, void or expired. A form is active when firstprinted. A form becomes frozen once it is signed. A form becomessubmitted once one of its submission hyperlinks has been activated,unless the hyperlink has its “submit delta” attribute set. A formbecomes void when the user invokes a void form, reset form or duplicateform page command. A form expires when the time the form has been activeexceeds the form's specified lifetime. While the form is active, forminput is allowed. Input through a form which is not active is insteadcaptured in the background field 833 of the relevant page instance.

When the form is active or frozen, form submission is allowed. Anyattempt to submit a form when the form is not active or frozen isrejected, and instead elicits an form status report.

Each form instance is associated (at 59) with any form instances derivedfrom it, thus providing a version history. This allows all but thelatest version of a form in a particular time period to be excluded froma search.

All input is captured as digital ink. Digital ink 873 consists of a setof timestamped stroke groups 874, each of which consists of a set ofstyled strokes 875. Each stroke consists of a set of timestamped penpositions 876, each of which also includes pen orientation and nibforce. The digital ink class diagram is shown in FIG. 33.

A field element 845 can be a checkbox field 877, a text field 878, adrawing field 879, or a signature field 880. The field element classdiagram is shown in FIG. 34. Any digital ink captured in a field's zone58 is assigned to the field.

A checkbox field has an associated boolean value 881, as shown in FIG.35. Any mark (a tick, a cross, a stroke, a fill zigzag, etc.) capturedin a checkbox field's zone causes a true value to be assigned to thefield's value.

A text field has an associated text value 882, as shown in FIG. 36. Anydigital ink captured in a text field's zone is automatically convertedto text via online handwriting recognition, and the text is assigned tothe field's value. Online handwriting recognition is well-understood(see for example Tappert, C., C. Y. Suen and T. Wakahara, “The State ofthe Art in On-Line Handwriting Recognition”, IEEE Transactions onPattern Analysis and Machine Intelligence, Vol. 12, No. 8, August 1990).

A signature field has an associated digital signature value 883, asshown in FIG. 37. Any digital ink captured in a signature field's zoneis automatically verified with respect to the identity of the owner ofthe pen, and a digital signature of the content of the form of which thefield is part is generated and assigned to the field's value. Thedigital signature is generated using the pen user's private signaturekey specific to the application which owns the form. Online signatureverification is well-understood (see for example Plamondon, R. and G.Lorette, “Automatic Signature Verification and Writer Identification—TheState of the Art”, Pattern Recognition, Vol. 22, No. 2, 1989).

A field element is hidden if its “hidden” attribute is set. A hiddenfield element does not have an input zone on a page and does not acceptinput. It can have an associated field value which is included in theform data when the form containing the field is submitted. “Editing”commands, such as strike-throughs indicating deletion, can also berecognized in form fields.

Because the handwriting recognition algorithm works “online” (i.e. withaccess to the dynamics of the pen movement), rather than “offline” (i.e.with access only to a bitmap of pen markings), it can recognize run-ondiscretely-written characters with relatively high accuracy, without awriter-dependent training phase. A writer-dependent model of handwritingis automatically generated over time, however, and can be generatedup-front if necessary,

Digital ink, as already stated, consists of a sequence of strokes. Anystroke which starts in a particular element's zone is appended to thatelement's digital ink stream, ready for interpretation. Any stroke notappended to an object's digital ink stream is appended to the backgroundfield's digital ink stream.

Digital ink captured in the background field is interpreted as aselection gesture. Circumscription of one or more objects is generallyinterpreted as a selection of the circumscribed objects, although theactual interpretation is application-specific.

Table 2 summarizes these various pen interactions with a netpage.

TABLE 2 Summary of pen interactions with a netpage Object Type Pen inputAction Hyperlink General Click Submit action to application Form ClickSubmit form to application Selection Click Submit selection toapplication Form field Checkbox Any mark Assign true to field TextHandwriting Convert digital ink to text; assign text to field DrawingDigital ink Assign digital ink to field Signature Signature Verifydigital ink signature; generate digital signature of form; assigndigital signature to field None — Circum- Assign digital ink to currentscription selection

The system maintains a current selection for each pen. The selectionconsists simply of the most recent stroke captured in the backgroundfield. The selection is cleared after an inactivity timeout to ensurepredictable behavior.

The raw digital ink captured in every field is retained on the netpagepage server and is optionally transmitted with the form data when theform is submitted to the application. This allows the application tointerrogate the raw digital ink should it suspect the originalconversion, such as the conversion of handwritten text. This can, forexample, involve human intervention at the application level for formsthat fail certain application-specific consistency checks. As anextension to this, the entire background area of a form can bedesignated as a drawing field. The application can then decide, on thebasis of the presence of digital ink outside the explicit fields of theform, to route the form to a human operator, on the assumption that theuser may have indicated amendments to the filled-in fields outside ofthose fields.

FIG. 38 shows a flowchart of the process of handling pen input relativeto a netpage. The process consists of receiving (at 884) a stroke fromthe pen; identifying (at 885) the page instance 830 to which the page ID50 in the stroke refers; retrieving (at 886) the page description 5;identifying (at 887) a formatted element 839 whose zone 58 the strokeintersects; determining (at 888) whether the formatted elementcorresponds to a field element, and if so appending (at 892) thereceived stroke to the digital ink of the field value 871, interpreting(at 893) the accumulated digital ink of the field, and determining (at894) whether the field is part of a hyperlinked group 866 and if soactivating (at 895) the associated hyperlink; alternatively determining(at 889) whether the formatted element corresponds to a hyperlinkelement and if so activating (at 895) the corresponding hyperlink;alternatively, in the absence of an input field or hyperlink, appending(at 890) the received stroke to the digital ink of the background field833; and copying (at 891) the received stroke to the current selection826 of the current pen, as maintained by the registration server.

FIG. 38 a shows a detailed flowchart of step 893 in the process shown inFIG. 38, where the accumulated digital ink of a field is interpretedaccording to the type of the field. The process consists of determining(at 896) whether the field is a checkbox and (at 897) whether thedigital ink represents a checkmark, and if so assigning (at 898) a truevalue to the field value; alternatively determining (at 899) whether thefield is a text field and if so converting (at 900) the digital ink tocomputer text, with the help of the appropriate registration server, andassigning (at 901) the converted computer text to the field value;alternatively determining (at 902) whether the field is a signaturefield and if so verifying (at 903) the digital ink as the signature ofthe pen's owner, with the help of the appropriate registration server,creating (at 904) a digital signature of the contents of thecorresponding form, also with the help of the registration server andusing the pen owner's private signature key relating to thecorresponding application, and assigning (at 905) the digital signatureto the field value.

1.7.3 Page Server Commands

A page server command is a command which is handled locally by the pageserver. It operates directly on form, page and document instances.

A page server command 907 can be a void form command 908, a duplicateform command 909, a reset form command 910, a get form status command911, a duplicate page command 912, a reset page command 913, a get pagestatus command 914, a duplicate document command 915, a reset documentcommand 916, or a get document status command 917, as shown in FIG. 39.

A void form command voids the corresponding form instance. A duplicateform command voids the corresponding form instance and then produces anactive printed copy of the current form instance with field valuespreserved. The copy contains the same hyperlink transaction IDs as theoriginal, and so is indistinguishable from the original to anapplication. A reset form command voids the corresponding form instanceand then produces an active printed copy of the form instance with fieldvalues discarded. A get form status command produces a printed report onthe status of the corresponding form instance, including who publishedit, when it was printed, for whom it was printed, and the form status ofthe form instance.

Since a form hyperlink instance contains a transaction ID, theapplication has to be involved in producing a new form instance. Abutton requesting a new form instance is therefore typically implementedas a hyperlink.

A duplicate page command produces a printed copy of the correspondingpage instance with the background field value preserved. If the pagecontains a form or is part of a form, then the duplicate page command isinterpreted as a duplicate form command. A reset page command produces aprinted copy of the corresponding page instance with the backgroundfield value discarded. If the page contains a form or is part of a form,then the reset page command is interpreted as a reset form command. Aget page status command produces a printed report on the status of thecorresponding page instance, including who published it, when it wasprinted, for whom it was printed, and the status of any forms itcontains or is part of.

The netpage logo which appears on every netpage is usually associatedwith a duplicate page element.

When a page instance is duplicated with field values preserved, fieldvalues are printed in their native form, i.e. a checkmark appears as astandard checkmark graphic, and text appears as typeset text. Onlydrawings and signatures appear in their original form, with a signatureaccompanied by a standard graphic indicating successful signatureverification.

A duplicate document command produces a printed copy of thecorresponding document instance with background field values preserved.If the document contains any forms, then the duplicate document commandduplicates the forms in the same way a duplicate form command does. Areset document command produces a printed copy of the correspondingdocument instance with background field values discarded. If thedocument contains any forms, then the reset document command resets theforms in the same way a reset form command does. A get document statuscommand produces a printed report on the status of the correspondingdocument instance, including who published it, when it was printed, forwhom it was printed, and the status of any forms it contains.

If the page server command's “on selected” attribute is set, then thecommand operates on the page identified by the pen's current selectionrather than on the page containing the command. This allows a menu ofpage server commands to be printed. If the target page doesn't contain apage server command element for the designated page server command, thenthe command is ignored.

An application can provide application-specific handling by embeddingthe relevant page server command element in a hyperlinked group. Thepage server activates the hyperlink associated with the hyperlinkedgroup rather than executing the page server command.

A page server command element is hidden if its “hidden” attribute isset. A hidden command element does not have an input zone on a page andso cannot be activated directly by a user. It can, however, be activatedvia a page server command embedded in a different page, if that pageserver command has its “on selected” attribute set.

1.8 Standard Features of Netpages

In the preferred form, each netpage is printed with the netpage logo atthe bottom to indicate that it is a netpage and therefore hasinteractive properties. The logo also acts as a copy button. In mostcases pressing the logo produces a copy of the page. In the case of aform, the button produces a copy of the entire form. And in the case ofa secure document, such as a ticket or coupon, the button elicits anexplanatory note or advertising page.

The default single-page copy function is handled directly by therelevant netpage page server. Special copy functions are handled bylinking the logo button to an application.

1.9 User Help System

In a preferred embodiment, the netpage printer has a single buttonlabelled “Help”. When pressed it elicits a single page of information,including:

-   -   status of printer connection    -   status of printer consumables    -   top-level help menu    -   document function menu    -   top-level netpage network directory

The help menu provides a hierarchical manual on how to use the netpagesystem.

The document function menu includes the following functions:

-   -   print a copy of a document    -   print a clean copy of a form    -   print the status of a document

A document function is initiated by simply pressing the button and thentouching any page of the document. The status of a document indicateswho published it and when, to whom it was delivered, and to whom andwhen it was subsequently submitted as a form.

The netpage network directory allows the user to navigate the hierarchyof publications and services on the network. As an alternative, the usercan call the netpage network “900” number “yellow pages” and speak to ahuman operator. The operator can locate the desired document and routeit to the user's printer. Depending on the document type, the publisheror the user pays the small “yellow pages” service fee.

The help page is obviously unavailable if the printer is unable toprint. In this case the “error” light is lit and the user can requestremote diagnosis over the network.

2 Personalized Publication Model

In the following description, news is used as a canonical publicationexample to illustrate personalization mechanisms in the netpage system.Although news is often used in the limited sense of newspaper andnewsmagazine news, the intended scope in the present context is wider.

In the netpage system, the editorial content and the advertising contentof a news publication are personalized using different mechanisms. Theeditorial content is personalized according to the reader's explicitlystated and implicitly captured interest profile. The advertising contentis personalized according to the reader's locality and demographic.

2.1 Editorial Personalization

A subscriber can draw on two kinds of news sources: those that delivernews publications, and those that deliver news streams. While newspublications are aggregated and edited by the publisher, news streamsare aggregated either by a news publisher or by a specialized newsaggregator. News publications typically correspond to traditionalnewspapers and newsmagazines, while news streams can be many and varied:a “raw” news feed from a news service, a cartoon strip, a freelancewriter's column, a friend's bulletin board, or the reader's own e-mail.

The netpage publication server supports the publication of edited newspublications as well as the aggregation of multiple news streams. Byhandling the aggregation and hence the formatting of news streamsselected directly by the reader, the server is able to place advertisingon pages over which it otherwise has no editorial control.

The subscriber builds a daily newspaper by selecting one or morecontributing news publications, and creating a personalized version ofeach. The resulting daily editions are printed and bound together into asingle newspaper. The various members of a household typically expresstheir different interests and tastes by selecting different dailypublications and then customizing them.

For each publication, the reader optionally selects specific sections.Some sections appear daily, while others appear weekly. The dailysections available from The New York Times online, for example, include“Page One Plus”, “National”, “International”, “Opinion”, “Business”,“Arts/Living”, “Technology”, and “Sports”. The set of available sectionsis specific to a publication, as is the default subset.

The reader can extend the daily newspaper by creating custom sections,each one drawing on any number of news streams. Custom sections might becreated for e-mail and friends' announcements (“Personal”), or formonitoring news feeds for specific topics (“Alerts” or “Clippings”).

For each section, the reader optionally specifies its size, eitherqualitatively (e.g. short, medium, or long), or numerically (i.e. as alimit on its number of pages), and the desired proportion ofadvertising, either qualitatively (e.g. high, normal, low, none), ornumerically (i.e. as a percentage).

The reader also optionally expresses a preference for a large number ofshorter articles or a small number of longer articles. Each article isideally written (or edited) in both short and long forms to support thispreference.

An article may also be written (or edited) in different versions tomatch the expected sophistication of the reader, for example to providechildren's and adults' versions. The appropriate version is selectedaccording to the reader's age. The reader can specify a “reading age”which takes precedence over their biological age.

The articles which make up each section are selected and prioritized bythe editors, and each is assigned a useful lifetime. By default they aredelivered to all relevant subscribers, in priority order, subject tospace constraints in the subscribers' editions.

In sections where it is appropriate, the reader may optionally enablecollaborative filtering. This is then applied to articles which have asufficiently long lifetime. Each article which qualifies forcollaborative filtering is printed with rating buttons at the end of thearticle. The buttons can provide an easy choice (e.g. “liked” and“disliked’), making it more likely that readers will bother to rate thearticle.

Articles with high priorities and short lifetimes are thereforeeffectively considered essential reading by the editors and aredelivered to most relevant subscribers.

The reader optionally specifies a serendipity factor, eitherqualitatively (e.g. do or don't surprise me), or numerically. A highserendipity factor lowers the threshold used for matching duringcollaborative filtering. A high factor makes it more likely that thecorresponding section will be filled to the reader's specified capacity.A different serendipity factor can be specified for different days ofthe week.

The reader also optionally specifies topics of particular interestwithin a section, and this modifies the priorities assigned by theeditors.

The speed of the reader's Internet connection affects the quality atwhich images can be delivered. The reader optionally specifies apreference for fewer images or smaller images or both. If the number orsize of images is not reduced, then images may be delivered at lowerquality (i.e. at lower resolution or with greater compression).

At a global level, the reader specifies how quantities, dates, times andmonetary values are localized. This involves specifying whether unitsare imperial or metric, a local timezone and time format, and a localcurrency, and whether the localization consist of in situ translation orannotation. These preferences are derived from the reader's locality bydefault.

To reduce reading difficulties caused by poor eyesight, the readeroptionally specifies a global preference for a larger presentation. Bothtext and images are scaled accordingly, and less information isaccommodated on each page.

The language in which a news publication is published, and itscorresponding text encoding, is a property of the publication and not apreference expressed by the user. However, the netpage system can beconfigured to provide automatic translation services in various guises.

2.2 Advertising Localization and Targeting

The personalization of the editorial content directly affects theadvertising content, because advertising is typically placed to exploitthe editorial context. Travel ads, for example, are more likely toappear in a travel section than elsewhere. The value of the editorialcontent to an advertiser (and therefore to the publisher) lies in itsability to attract large numbers of readers with the right demographics.

Effective advertising is placed on the basis of locality anddemographics. Locality determines proximity to particular services,retailers etc., and particular interests and concerns associated withthe local community and environment. Demographics determine generalinterests and preoccupations as well as likely spending patterns.

A news publisher's most profitable product is advertising “space”, amulti-dimensional entity determined by the publication's geographiccoverage, the size of its readership, its readership demographics, andthe page area available for advertising.

In the netpage system, the netpage publication server computes theapproximate multi-dimensional size of a publication's saleableadvertising space on a per-section basis, taking into account thepublication's geographic coverage, the section's readership, the size ofeach reader's section edition, each reader's advertising proportion, andeach reader's demographic.

In comparison with other media, the netpage system allows theadvertising space to be defined in greater detail, and allows smallerpieces of it to be sold separately. It therefore allows it to be sold atcloser to its true value.

For example, the same advertising “slot” can be sold in varyingproportions to several advertisers, with individual readers' pagesrandomly receiving the advertisement of one advertiser or another,overall preserving the proportion of space sold to each advertiser.

The netpage system allows advertising to be linked directly to detailedproduct information and online purchasing. It therefore raises theintrinsic value of the advertising space.

Because personalization and localization are handled automatically bynetpage publication servers, an advertising aggregator can providearbitrarily broad coverage of both geography and demographics. Thesubsequent disaggregation is efficient because it is automatic. Thismakes it more cost-effective for publishers to deal with advertisingaggregators than to directly capture advertising. Even though theadvertising aggregator is taking a proportion of advertising revenue,publishers may find the change profit-neutral because of the greaterefficiency of aggregation. The advertising aggregator acts as anintermediary between advertisers and publishers, and may place the sameadvertisement in multiple publications.

It is worth noting that ad placement in a netpage publication can bemore complex than ad placement in the publication's traditionalcounterpart, because the publication's advertising space is morecomplex. While ignoring the full complexities of negotiations betweenadvertisers, advertising aggregators and publishers, the preferred formof the netpage system provides some automated support for thesenegotiations, including support for automated auctions of advertisingspace. Automation is particularly desirable for the placement ofadvertisements which generate small amounts of income, such as small orhighly localized advertisements.

Once placement has been negotiated, the aggregator captures and editsthe advertisement and records it on a netpage ad server.Correspondingly, the publisher records the ad placement on the relevantnetpage publication server. When the netpage publication server lays outeach user's personalized publication, it picks the relevantadvertisements from the netpage ad server.

2.3 User Profiles

2.3.1 Information Filtering

The personalization of news and other publications relies on anassortment of user-specific profile information, including:

-   -   publication customizations    -   collaborative filtering vectors    -   contact details    -   presentation preferences

The customization of a publication is typically publication-specific,and so the customization information is maintained by the relevantnetpage publication server.

A collaborative filtering vector consists of the user's ratings of anumber of news items. It is used to correlate different users' interestsfor the purposes of making recommendations. Although there are benefitsto maintaining a single collaborative filtering vector independently ofany particular publication, there are two reasons why it is morepractical to maintain a separate vector for each publication: there islikely to be more overlap between the vectors of subscribers to the samepublication than between those of subscribers to different publications;and a publication is likely to want to present its users' collaborativefiltering vectors as part of the value of its brand, not to be foundelsewhere. Collaborative filtering vectors are therefore also maintainedby the relevant netpage publication server.

Contact details, including name, street address, ZIP Code, state,country, telephone numbers, are global by nature, and are maintained bya netpage registration server.

Presentation preferences, including those for quantities, dates andtimes, are likewise global and maintained in the same way.

The localization of advertising relies on the locality indicated in theuser's contact details, while the targeting of advertising relies onpersonal information such as date of birth, gender, marital status,income, profession, education, or qualitative derivatives such as agerange and income range.

For those users who choose to reveal personal information foradvertising purposes, the information is maintained by the relevantnetpage registration server. In the absence of such information,advertising can be targeted on the basis of the demographic associatedwith the user's ZIP or ZIP+4 Code.

Each user, pen, printer, application provider and application isassigned its own unique identifier, and the netpage registration servermaintains the relationships between them, as shown in FIGS. 21, 22, 23and 24. For registration purposes, a publisher is a special kind ofapplication provider, and a publication is a special kind ofapplication.

Each user 800 may be authorized to use any number of printers 802, andeach printer may allow any number of users to use it. Each user has asingle default printer (at 66), to which periodical publications aredelivered by default, whilst pages printed on demand are delivered tothe printer through which the user is interacting. The server keepstrack of which publishers a user has authorized to print to the user'sdefault printer. A publisher does not record the ID of any particularprinter, but instead resolves the ID when it is required.

When a user subscribes 808 to a publication 807, the publisher 806 (i.e.application provider 803) is authorized to print to a specified printeror the user's default printer. This authorization can be revoked at anytime by the user. Each user may have several pens 801, but a pen isspecific to a single user. If a user is authorized to use a particularprinter, then that printer recognizes any of the user's pens.

The pen ID is used to locate the corresponding user profile maintainedby a particular netpage registration server, via the DNS in the usualway.

A Web terminal 809 can be authorized to print on a particular netpageprinter, allowing Web pages and netpage documents encountered during Webbrowsing to be conveniently printed on the nearest netpage printer.

The netpage system can collect, on behalf of a printer provider, feesand commissions on income earned through publications printed on theprovider's printers. Such income can include advertising fees,click-through fees, e-commerce commissions, and transaction fees. If theprinter is owned by the user, then the user is the printer provider.

Each user also has a netpage account 820 which is used to accumulatemicro-debits and credits (such as those described in the precedingparagraph); contact details 815, including name, address and telephonenumbers; global preferences 816, including privacy, delivery andlocalization settings; any number of biometric records 817, containingthe user's encoded signature 818, fingerprint 819 etc; a handwritingmodel 819 automatically maintained by the system; and SET payment cardaccounts 821 with which e-commerce payments can be made.

2.3.2 Favorites List

A netpage user can maintain a list 922 of “favorites”—links to usefuldocuments etc. on the netpage network. The list is maintained by thesystem on the user's behalf. It is organized as a hierarchy of folders924, a preferrred embodiment of which is shown in the class diagram inFIG. 41.

2.3.3 History List

The system maintains a history list 929 on each user's behalf,containing links to documents etc. accessed by the user through thenetpage system. It is organized as a date-ordered list, a preferredembodiment of which is shown in the class diagram in FIG. 42.

2.4 Intelligent Page Layout

The netpage publication server automatically lays out the pages of eachuser's personalized publication on a section-by-section basis. Sincemost advertisements are in the form of pre-formatted rectangles, theyare placed on the page before the editorial content.

The advertising ratio for a section can be achieved with wildly varyingadvertising ratios on individual pages within the section, and the adlayout algorithm exploits this. The algorithm is configured to attemptto co-locate closely tied editorial and advertising content, such asplacing ads for roofing material specifically within the publicationbecause of a special feature on do-it-yourself roofing repairs.

The editorial content selected for the user, including text andassociated images and graphics, is then laid out according to variousaesthetic rules.

The entire process, including the selection of ads and the selection ofeditorial content, must be iterated once the layout has converged, toattempt to more closely achieve the user's stated section sizepreference. The section size preference can, however, be matched onaverage over time, allowing significant day-to-day variations.

2.5 Document Format

Once the document is laid out, it is encoded for efficient distributionand persistent storage on the netpage network.

The primary efficiency mechanism is the separation of informationspecific to a single user's edition and information shared betweenmultiple users' editions. The specific information consists of the pagelayout. The shared information consists of the objects to which the pagelayout refers, including images, graphics, and pieces of text.

A text object contains fully-formatted text represented in theExtensible Markup Language (XML) using the Extensible StylesheetLanguage (XSL). XSL provides precise control over text formattingindependently of the region into which the text is being set, which inthis case is being provided by the layout. The text object containsembedded language codes to enable automatic translation, and embeddedhyphenation hints to aid with paragraph formatting.

An image object encodes an image in the JPEG 2000 wavelet-basedcompressed image format. A graphic object encodes a 2D graphic inScalable Vector Graphics (SVG) format.

The layout itself consists of a series of placed image and graphicobjects, linked textflow objects through which text objects flow,hyperlinks and input fields as described above, and watermark regions.These layout objects are summarized in Table 3. The layout uses acompact format suitable for efficient distribution and storage.

TABLE 3 netpage layout objects Layout object Attribute Format of linkedobject Image Position — Image object ID JPEG 2000 Graphic Position —Graphic object ID SVG Textflow Textflow ID — Zone — Optional text objectID XML/XSL Hyperlink Type — Zone — Application ID, etc. — Field Type —Meaning — Zone — Watermark Zone —2.6 Document Distribution

As described above, for purposes of efficient distribution andpersistent storage on the netpage network, a user-specific page layoutis separated from the shared objects to which it refers.

When a subscribed publication is ready to be distributed, the netpagepublication server allocates, with the help of the netpage ID server 12,a unique ID for each page, page instance, document, and documentinstance.

The server computes a set of optimized subsets of the shared content andcreates a multicast channel for each subset, and then tags eachuser-specific layout with the names of the multicast channels which willcarry the shared content used by that layout. The server then pointcastseach user's layouts to that user's printer via the appropriate pageserver, and when the pointcasting is complete, multicasts the sharedcontent on the specified channels. After receiving its pointcast, eachpage server and printer subscribes to the multicast channels specifiedin the page layouts. During the multicasts, each page server and printerextracts from the multicast streams those objects referred to by itspage layouts. The page servers persistently archive the received pagelayouts and shared content.

Once a printer has received all the objects to which its page layoutsrefer, the printer re-creates the fully-populated layout and thenrasterizes and prints it.

Under normal circumstances, the printer prints pages faster than theycan be delivered. Assuming a quarter of each page is covered withimages, the average page has a size of less than 400 KB. The printer cantherefore hold in excess of 100 such pages in its internal 64 MB memory,allowing for temporary buffers etc. The printer prints at a rate of onepage per second. This is equivalent to 400 KB or about 3 Mbit of pagedata per second, which is similar to the highest expected rate of pagedata delivery over a broadband network.

Even under abnormal circumstances, such as when the printer runs out ofpaper, it is likely that the user will be able to replenish the papersupply before the printer's 100-page internal storage capacity isexhausted.

However, if the printer's internal memory does fill up, then the printerwill be unable to make use of a multicast when it first occurs. Thenetpage publication server therefore allows printers to submit requestsfor re-multicasts. When a critical number of requests is received or atimeout occurs, the server re-multicasts the corresponding sharedobjects.

Once a document is printed, a printer can produce an exact duplicate atany time by retrieving its page layouts and contents from the relevantpage server.

2.7 On-Demand Documents

When a netpage document is requested on demand, it can be personalizedand delivered in much the same way as a periodical. However, since thereis no shared content, delivery is made directly to the requestingprinter without the use of multicast.

When a non-netpage document is requested on demand, it is notpersonalized, and it is delivered via a designated netpage formattingserver which reformats it as a netpage document. A netpage formattingserver is a special instance of a netpage publication server. Thenetpage formatting server has knowledge of various Internet documentformats, including Adobe's Portable Document Format (PDF), and HypertextMarkup Language (HTML). In the case of HTML, it can make use of thehigher resolution of the printed page to present Web pages in amulti-column format, with a table of contents. It can automaticallyinclude all Web pages directly linked to the requested page. The usercan tune this behavior via a preference.

The netpage formatting server makes standard netpage behavior, includinginteractivity and persistence, available on any Internet document, nomatter what its origin and format. It hides knowledge of differentdocument formats from both the netpage printer and the netpage pageserver, and hides knowledge of the netpage system from Web servers.

3 Security

3.1 Cryptography

Cryptography is used to protect sensitive information, both in storageand in transit, and to authenticate parties to a transaction. There aretwo classes of cryptography in widespread use: secret-key cryptographyand public-key cryptography. The netpage network uses both classes ofcryptography.

Secret-key cryptography, also referred to as symmetric cryptography,uses the same key to encrypt and decrypt a message. Two parties wishingto exchange messages must first arrange to securely exchange the secretkey.

Public-key cryptography, also referred to as asymmetric cryptography,uses two encryption keys. The two keys are mathematically related insuch a way that any message encrypted using one key can only bedecrypted using the other key. One of these keys is then published,while the other is kept private. The public key is used to encrypt anymessage intended for the holder of the private key. Once encrypted usingthe public key, a message can only be decrypted using the private key.Thus two parties can securely exchange messages without first having toexchange a secret key. To ensure that the private key is secure, it isnormal for the holder of the private key to generate the key pair.

Public-key cryptography can be used to create a digital signature. Theholder of the private key can create a known hash of a message and thenencrypt the hash using the private key. Anyone can then verify that theencrypted hash constitutes the “signature” of the holder of the privatekey with respect to that particular message by decrypting the encryptedhash using the public key and verifying the hash against the message. Ifthe signature is appended to the message, then the recipient of themessage can verify both that the message is genuine and that it has notbeen altered in transit.

To make public-key cryptography work, there has to be a way todistribute public keys which prevents impersonation. This is normallydone using certificates and certificate authorities. A certificateauthority is a trusted third party which authenticates the connectionbetween a public key and someone's identity. The certificate authorityverifies the person's identity by examining identity documents, and thencreates and signs a digital certificate containing the person's identitydetails and public key. Anyone who trusts the certificate authority canuse the public key in the certificate with a high degree of certaintythat it is genuine. They just have to verify that the certificate hasindeed been signed by the certificate authority, whose public key iswell-known.

In most transaction environments, public-key cryptography is only usedto create digital signatures and to securely exchange secret sessionkeys. Secret-key cryptography is used for all other purposes.

In the following discussion, when reference is made to the securetransmission of information between a netpage printer and a server, whatactually happens is that the printer obtains the server's certificate,authenticates it with reference to the certificate authority, uses thepublic key-exchange key in the certificate to exchange a secret sessionkey with the server, and then uses the secret session key to encrypt themessage data. A session key, by definition, can have an arbitrarilyshort lifetime.

3.2 Netpage Printer Security

Each netpage printer is assigned a pair of unique identifiers at time ofmanufacture which are stored in read-only memory in the printer and inthe netpage registration server database. The first ID 62 is public anduniquely identifies the printer on the netpage network. The second ID issecret and is used when the printer is first registered on the network.

When the printer connects to the netpage network for the first timeafter installation, it creates a signature public/private key pair. Ittransmits the secret ID and the public key securely to the netpageregistration server. The server compares the secret ID against theprinter's secret ID recorded in its database, and accepts theregistration if the IDs match. It then creates and signs a certificatecontaining the printer's public ID and public signature key, and storesthe certificate in the registration database.

The netpage registration server acts as a certificate authority fornetpage printers, since it has access to secret information allowing itto verify printer identity.

When a user subscribes to a publication, a record is created in thenetpage registration server database authorizing the publisher to printthe publication to the user's default printer or a specified printer.Every document sent to a printer via a page server is addressed to aparticular user and is signed by the publisher using the publisher'sprivate signature key. The page server verifies, via the registrationdatabase, that the publisher is authorized to deliver the publication tothe specified user. The page server verifies the signature using thepublisher's public key, obtained from the publisher's certificate storedin the registration database.

The netpage registration server accepts requests to add printingauthorizations to the database, so long as those requests are initiatedvia a pen registered to the printer.

3.3 Netpage Pen Security

Each netpage pen is assigned a unique identifier at time of manufacturewhich is stored in read-only memory in the pen and in the netpageregistration server database. The pen ID 61 uniquely identifies the penon the netpage network.

A netpage pen can “know” a number of netpage printers, and a printer can“know” a number of pens. A pen communicates with a printer via a radiofrequency signal whenever it is within range of the printer. Once a penand printer are registered, they regularly exchange session keys.Whenever the pen transmits digital ink to the printer, the digital inkis always encrypted using the appropriate session key. Digital ink isnever transmitted in the clear.

A pen stores a session key for every printer it knows, indexed byprinter ID, and a printer stores a session key for every pen it knows,indexed by pen ID. Both have a large but finite storage capacity forsession keys, and will forget a session key on a least-recently-usedbasis if necessary.

When a pen comes within range of a printer, the pen and printer discoverwhether they know each other. If they don't know each other, then theprinter determines whether it is supposed to know the pen. This mightbe, for example, because the pen belongs to a user who is registered touse the printer. If the printer is meant to know the pen but doesn't,then it initiates the automatic pen registration procedure. If theprinter isn't meant to know the pen, then it agrees with the pen toignore it until the pen is placed in a charging cup, at which time itinitiates the registration procedure.

In addition to its public ID, the pen contains a secret key-exchangekey. The key-exchange key is also recorded in the netpage registrationserver database at time of manufacture. During registration, the pentransmits its pen ID to the printer, and the printer transmits the penID to the netpage registration server. The server generates a sessionkey for the printer and pen to use, and securely transmits the sessionkey to the printer. It also transmits a copy of the session keyencrypted with the pen's key-exchange key. The printer stores thesession key internally, indexed by the pen ID, and transmits theencrypted session key to the pen. The pen stores the session keyinternally, indexed by the printer ID.

Although a fake pen can impersonate a pen in the pen registrationprotocol, only a real pen can decrypt the session key transmitted by theprinter.

When a previously unregistered pen is first registered, it is of limiteduse until it is linked to a user. A registered but “un-owned” pen isonly allowed to be used to request and fill in netpage user and penregistration forms, to register a new user to which the new pen isautomatically linked, or to add a new pen to an existing user.

The pen uses secret-key rather than public-key encryption because ofhardware performance constraints in the pen.

3.4 Secure Documents

The netpage system supports the delivery of secure documents such astickets and coupons. The netpage printer includes a facility to printwatermarks, but will only do so on request from publishers who aresuitably authorized. The publisher indicates its authority to printwatermarks in its certificate, which the printer is able toauthenticate.

The “watermark” printing process uses an alternative dither matrix inspecified “watermark” regions of the page. Back-to-back pages containmirror-image watermark regions which coincide when printed. The dithermatrices used in odd and even pages' watermark regions are designed toproduce an interference effect when the regions are viewed together,achieved by looking through the printed sheet.

The effect is similar to a watermark in that it is not visible whenlooking at only one side of the page, and is lost when the page iscopied by normal means.

Pages of secure documents cannot be copied using the built-in netpagecopy mechanism described in Section 1.9 above. This extends to copyingnetpages on netpage-aware photocopiers.

Secure documents are typically generated as part of e-commercetransactions. They can therefore include the user's photograph which wascaptured when the user registered biometric information with the netpageregistration server, as described in Section 2.

When presented with a secure netpage document, the recipient can verifyits authenticity by requesting its status in the usual way. The uniqueID of a secure document is only valid for the lifetime of the document,and secure document IDs are allocated non-contiguously to prevent theirprediction by opportunistic forgers. A secure document verification pencan be developed with built-in feedback on verification failure, tosupport easy point-of-presentation document verification.

Clearly neither the watermark nor the user's photograph are secure in acryptographic sense. They simply provide a significant obstacle tocasual forgery. Online document verification, particularly using averification pen, provides an added level of security where it isneeded, but is still not entirely immune to forgeries.

3.5 Non-Repudiation

In the netpage system, forms submitted by users are delivered reliablyto forms handlers and are persistently archived on netpage page servers.It is therefore impossible for recipients to repudiate delivery.

E-commerce payments made through the system, as described in Section 4,are also impossible for the payee to repudiate.

4 Electronic Commerce Model

4.1 Secure Electronic Transaction (SET)

The netpage system uses the Secure Electronic Transaction (SET) systemas one of its payment systems. SET, having been developed by MasterCardand Visa, is organized around payment cards, and this is reflected inthe terminology. However, much of the system is independent of the typeof accounts being used.

In SET, cardholders and merchants register with a certificate authorityand are issued with certificates containing their public signature keys.The certificate authority verifies a cardholder's registration detailswith the card issuer as appropriate, and verifies a merchant'sregistration details with the acquirer as appropriate. Cardholders andmerchants store their respective private signature keys securely ontheir computers. During the payment process, these certificates are usedto mutually authenticate a merchant and cardholder, and to authenticatethem both to the payment gateway.

SET has not yet been adopted widely, partly because cardholdermaintenance of keys and certificates is considered burdensome. Interimsolutions which maintain cardholder keys and certificates on a serverand give the cardholder access via a password have met with somesuccess.

4.2 SET Payments

In the netpage system the netpage registration server acts as a proxyfor the netpage user (i.e. the cardholder) in SET payment transactions.

The netpage system uses biometrics to authenticate the user andauthorize SET payments. Because the system is pen-based, the biometricused is the user's on-line signature, consisting of time-varying penposition and pressure. A fingerprint biometric can also be used bydesigning a fingerprint sensor into the pen, although at a higher cost.The type of biometric used only affects the capture of the biometric,not the authorization aspects of the system.

The first step to being able to make SET payments is to register theuser's biometric with the netpage registration server. This is done in acontrolled environment, for example a bank, where the biometric can becaptured at the same time as the user's identity is verified. Thebiometric is captured and stored in the registration database, linked tothe user's record. The user's photograph is also optionally captured andlinked to the record. The SET cardholder registration process iscompleted, and the resulting private signature key and certificate arestored in the database. The user's payment card information is alsostored, giving the netpage registration server enough information to actas the user's proxy in any SET payment transaction.

When the user eventually supplies the biometric to complete a payment,for example by signing a netpage order form, the printer securelytransmits the order information, the pen ID and the biometric data tothe netpage registration server. The server verifies the biometric withrespect to the user identified by the pen ID, and from then on acts asthe user's proxy in completing the SET payment transaction.

4.3 Micro-Payments

The netpage system includes a mechanism for micro-payments, to allow theuser to be conveniently charged for printing low-cost documents ondemand and for copying copyright documents, and possibly also to allowthe user to be reimbursed for expenses incurred in printing advertisingmaterial. The latter depends on the level of subsidy already provided tothe user.

When the user registers for e-commerce, a network account is establishedwhich aggregates micro-payments. The user receives a statement on aregular basis, and can settle any outstanding debit balance using thestandard payment mechanism.

The network account can be extended to aggregate subscription fees forperiodicals, which would also otherwise be presented to the user in theform of individual statements.

4.4 Transactions

When a user requests a netpage in a particular application context, theapplication is able to embed a user-specific transaction ID 55 in thepage. Subsequent input through the page is tagged with the transactionID, and the application is thereby able to establish an appropriatecontext for the user's input.

When input occurs through a page which is not user-specific, however,the application must use the user's unique identity to establish acontext. A typical example involves adding items from a pre-printedcatalog page to the user's virtual “shopping cart”. To protect theuser's privacy, however, the unique user ID 60 known to the netpagesystem is not divulged to applications. This is to prevent differentapplication providers from easily correlating independently accumulatedbehavioral data.

The netpage registration server instead maintains an anonymousrelationship between a user and an application via a unique alias ID 65,as shown in FIG. 24. Whenever the user activates a hyperlink tagged withthe “registered” attribute, the netpage page server asks the netpageregistration server to translate the associated application ID 64,together with the pen ID 61, into an alias ID 65. The alias ID is thensubmitted to the hyperlink's application.

The application maintains state information indexed by alias ID, and isable to retrieve user-specific state information without knowledge ofthe global identity of the user.

The system also maintains an independent certificate and privatesignature key for each of a user's applications, to allow it to signapplication transactions on behalf of the user using onlyapplication-specific information.

To assist the system in routing product bar code (UPC) “hyperlink”activations, the system records a favorite application on behalf of theuser for any number of product types.

Each application is associated with an application provider, and thesystem maintains an account on behalf of each application provider, toallow it to credit and debit the provider for click-through fees etc.

An application provider can be a publisher of periodical subscribedcontent. The system records the user's willingness to receive thesubscribed publication, as well as the expected frequency ofpublication.

4.5 Resource Descriptions and Copyright

A preferred embodiment of a resource description class diagram is shownin FIG. 40. Each document and content object may be described by one ormore resource descriptions 842. Resource descriptions use the DublinCore metadata element set, which is designed to facilitate discovery ofelectronic resources. Dublin Core metadata conforms to the World WideWeb Consortium (W3C) Resource Description Framework (RDF).

A resource description may identify rights holders 920. The netpagesystem automatically transfers copyright fees from users to rightsholders when users print copyright content.

5 Communications Protocols

A communications protocol defines an ordered exchange of messagesbetween entities. In the netpage system, entities such as pens, printersand servers utilise a set of defined protocols to cooperatively handleuser interaction with the netpage system.

Each protocol is illustrated by way of a sequence diagram in which thehorizontal dimension is used to represent message flow and the verticaldimension is used to represent time. Each entity is represented by arectangle containing the name of the entity and a vertical columnrepresenting the lifeline of the entity. During the time an entityexists, the lifeline is shown as a dashed line. During the time anentity is active, the lifeline is shown as a double line. Because theprotocols considered here do not create or destroy entities, lifelinesare generally cut short as soon as an entity ceases to participate in aprotocol.

5.1 Subscription Delivery Protocol

A preferred embodiment of a subscription delivery protocol is shown inFIG. 43.

A large number of users may subscribe to a periodical publication. Eachuser's edition may be laid out differently, but many users' editionswill share common content such as text objects and image objects. Thesubscription delivery protocol therefore delivers document structures toindividual printers via pointcast, but delivers shared content objectsvia multicast.

The application (i.e. publisher) first obtains a document ID 51 for eachdocument from an ID server 12. It then sends each document structure,including its document ID and page descriptions, to the page server 10responsible for the document's newly allocated ID. It includes its ownapplication ID 64, the subscriber's alias ID 65, and the relevant set ofmulticast channel names. It signs the message using its privatesignature key.

The page server uses the application ID and alias ID to obtain from theregistration server the corresponding user ID 60, the user's selectedprinter ID 62 (which may be explicitly selected for the application, ormay be the user's default printer), and the application's certificate.

The application's certificate allows the page server to verify themessage signature. The page server's request to the registration serverfails if the application ID and alias ID don't together identify asubscription 808.

The page server then allocates document and page instance IDs andforwards the page descriptions, including page IDs 50, to the printer.It includes the relevant set of multicast channel names for the printerto listen to.

It then returns the newly allocated page IDs to the application forfuture reference.

Once the application has distributed all of the document structures tothe subscribers' selected printers via the relevant page servers, itmulticasts the various subsets of the shared objects on the previouslyselected multicast channels. Both page servers and printers monitor theappropriate multicast channels and receive their required contentobjects. They are then able to populate the previously pointcastdocument structures. This allows the page servers to add completedocuments to their databases, and it allows the printers to print thedocuments.

5.2 Hyperlink Activation Protocol

A preferred embodiment of a hyperlink activation protocol is shown inFIG. 45.

When a user clicks on a netpage with a netpage pen, the pen communicatesthe click to the nearest netpage printer 601. The click identifies thepage and a location on the page. The printer already knows the ID 61 ofthe pen from the pen connection protocol.

The printer determines, via the DNS, the network address of the pageserver 10 a handling the particular page ID 50. The address may alreadybe in its cache if the user has recently interacted with the same page.The printer then forwards the pen ID, its own printer ID 62, the page IDand click location to the page server.

The page server loads the page description 5 identified by the page IDand determines which input element's zone 58, if any, the click lies in.Assuming the relevant input element is a hyperlink element 844, the pageserver then obtains the associated application ID 64 and link ID 54, anddetermines, via the DNS, the network address of the application serverhosting the application 71.

The page server uses the pen ID 61 to obtain the corresponding user ID60 from the registration server 11, and then allocates a globally uniquehyperlink request ID 52 and builds a hyperlink request 934. Thehyperlink request class diagram is shown in FIG. 44. The hyperlinkrequest records the IDs of the requesting user and printer, andidentifies the clicked hyperlink instance 862. The page server thensends its own server ID 53, the hyperlink request ID, and the link ID tothe application.

The application produces a response document according toapplication-specific logic, and obtains a document ID 51 from an IDserver 12. It then sends the document to the page server 10 bresponsible for the document's newly allocated ID, together with therequesting page server's ID and the hyperlink request ID.

The second page server sends the hyperlink request ID and application IDto the first page server to obtain the corresponding user ID and printerID 62. The first page server rejects the request if the hyperlinkrequest has expired or is for a different application.

The second page server allocates document instance and page IDs 50,returns the newly allocated page IDs to the application, adds thecomplete document to its own database, and finally sends the pagedescriptions to the requesting printer.

The hyperlink instance may include a meaningful transaction ID 55, inwhich case the first page server includes the transaction ID in themessage sent to the application. This allows the application toestablish a transaction-specific context for the hyperlink activation.

If the hyperlink requires a user alias, i.e. its “alias required”attribute is set, then the first page server sends both the pen ID 61and the hyperlink's application ID 64 to the registration server 11 toobtain not just the user ID corresponding to the pen ID but also thealias ID 65 corresponding to the application ID and the user ID. Itincludes the alias ID in the message sent to the application, allowingthe application to establish a user-specific context for the hyperlinkactivation.

5.3 Handwriting Recognition Protocol

When a user draws a stroke on a netpage with a netpage pen, the pencommunicates the stroke to the nearest netpage printer. The strokeidentifies the page and a path on the page.

The printer forwards the pen ID 61, its own printer ID 62, the page ID50 and stroke path to the page server 10 in the usual way.

The page server loads the page description 5 identified by the page IDand determines which input element's zone 58, if any, the strokeintersects. Assuming the relevant input element is a text field 878, thepage server appends the stroke to the text field's digital ink.

After a period of inactivity in the zone of the text field, the pageserver sends the pen ID and the pending strokes to the registrationserver 11 for interpretation. The registration server identifies theuser corresponding to the pen, and uses the user's accumulatedhandwriting model 822 to interpret the strokes as handwritten text. Onceit has converted the strokes to text, the registration server returnsthe text to the requesting page server. The page server appends the textto the text value of the text field.

5.4 Signature Verification Protocol

Assuming the input element whose zone the stroke intersects is asignature field 880, the page server 10 appends the stroke to thesignature field's digital ink.

After a period of inactivity in the zone of the signature field, thepage server sends the pen ID 61 and the pending strokes to theregistration server 11 for verification. It also sends the applicationID 64 associated with the form of which the signature field is part, aswell as the form ID 56 and the current data content of the form. Theregistration server identifies the user corresponding to the pen, anduses the user's dynamic signature biometric 818 to verify the strokes asthe user's signature. Once it has verified the signature, theregistration server uses the application ID 64 and user ID 60 toidentify the user's application-specific private signature key. It thenuses the key to generate a digital signature of the form data, andreturns the digital signature to the requesting page server. The pageserver assigns the digital signature to the signature field and sets theassociated form's status to frozen.

The digital signature includes the alias ID 65 of the correspondinguser. This allows a single form to capture multiple users' signatures.

5.5 Form Submission Protocol

A preferred embodiment of a form submission protocol is shown in FIG.46.

Form submission occurs via a form hyperlink activation. It thus followsthe protocol defined in Section 5.2, with some form-specific additions.

In the case of a form hyperlink, the hyperlink activation message sentby the page server 10 to the application 71 also contains the form ID 56and the current data content of the form. If the form contains anysignature fields, then the application verifies each one by extractingthe alias ID 65 associated with the corresponding digital signature andobtaining the corresponding certificate from the registration server 11.

5.6 Commission Payment Protocol

A preferred embodiment of a commission payment protocol is shown in FIG.47.

In an e-commerce environment, fees and commissions may be payable froman application provider to a publisher on click-throughs, transactionsand sales. Commissions on fees and commissions on commissions may alsobe payable from the publisher to the provider of the printer.

The hyperlink request ID 52 is used to route a fee or commission creditfrom the target application provider 70 a (e.g. merchant) to the sourceapplication provider 70 b (i.e. publisher), and from the sourceapplication provider 70 b to the printer provider 72.

The target application receives the hyperlink request ID from the pageserver 10 when the hyperlink is first activated, as described in Section5.2. When the target application needs to credit the source applicationprovider, it sends the application provider credit to the original pageserver together with the hyperlink request ID. The page server uses thehyperlink request ID to identify the source application, and sends thecredit on to the relevant registration server 11 together with thesource application ID 64, its own server ID 53, and the hyperlinkrequest ID. The registration server credits the correspondingapplication provider's account 827. It also notifies the applicationprovider.

If the application provider needs to credit the printer provider, itsends the printer provider credit to the original page server togetherwith the hyperlink request ID. The page server uses the hyperlinkrequest ID to identify the printer, and sends the credit on to therelevant registration server together with the printer ID. Theregistration server credits the corresponding printer provider account814.

The source application provider is optionally notified of the identityof the target application provider, and the printer provider of theidentity of the source application provider.

6. Netpage Pen Description

6.1 Pen Mechanics

Referring to FIGS. 8 and 9, the pen, generally designated by referencenumeral 101, includes a housing 102 in the form of a plastics mouldinghaving walls 103 defining an interior space 104 for mounting the pencomponents. The pen top 105 is in operation rotatably mounted at one end106 of the housing 102. A semi-transparent cover 107 is secured to theopposite end 108 of the housing 102. The cover 107 is also of mouldedplastics, and is formed from semi-transparent material in order toenable the user to view the status of the LED mounted within the housing102. The cover 107 includes a main part 109 which substantiallysurrounds the end 108 of the housing 102 and a projecting portion 110which projects back from the main part 109 and fits within acorresponding slot 111 formed in the walls 103 of the housing 102. Aradio antenna 112 is mounted behind the projecting portion 110, withinthe housing 102. Screw threads 113 surrounding an aperture 113A on thecover 107 are arranged to receive a metal end piece 114, includingcorresponding screw threads 115. The metal end piece 114 is removable toenable ink cartridge replacement.

Also mounted within the cover 107 is a tri-color status LED 116 on aflex PCB 117. The antenna 112 is also mounted on the flex PCB 117. Thestatus LED 116 is mounted at the top of the pen 101 for good all-aroundvisibility.

The pen can operate both as a normal marking ink pen and as anon-marking stylus. An ink pen cartridge 118 with nib 119 and a stylus120 with stylus nib 121 are mounted side by side within the housing 102.Either the ink cartridge nib 119 or the stylus nib 121 can be broughtforward through open end 122 of the metal end piece 114, by rotation ofthe pen top 105. Respective slider blocks 123 and 124 are mounted to theink cartridge 118 and stylus 120, respectively. A rotatable cam barrel125 is secured to the pen top 105 in operation and arranged to rotatetherewith. The cam barrel 125 includes a cam 126 in the form of a slotwithin the walls 181 of the cam barrel. Cam followers 127 and 128projecting from slider blocks 123 and 124 fit within the cam slot 126.On rotation of the cam barrel 125, the slider blocks 123 or 124 moverelative to each other to project either the pen nib 119 or stylus nib121 out through the hole 122 in the metal end piece 114. The pen 101 hasthree states of operation. By turning the top 105 through 90° steps, thethree states are:

-   -   Stylus 120 nib 121 out;    -   Ink cartridge 118 nib 119 out; and    -   Neither ink cartridge 118 nib 119 out nor stylus 120 nib 121        out.

A second flex PCB 129, is mounted on an electronics chassis 130 whichsits within the housing 102. The second flex PCB 129 mounts an infraredLED 131 for providing infrared radiation for projection onto thesurface. An image sensor 132 is provided mounted on the second flex PCB129 for receiving reflected radiation from the surface. The second flexPCB 129 also mounts a radio frequency chip 133, which includes an RFtransmitter and RF receiver, and a controller chip 134 for controllingoperation of the pen 101. An optics block 135 (formed from moulded clearplastics) sits within the cover 107 and projects an infrared beam ontothe surface and receives images onto the image sensor 132. Power supplywires 136 connect the components on the second flex PCB 129 to batterycontacts 137 which are mounted within the cam barrel 125. A terminal 138connects to the battery contacts 137 and the cam barrel 125. A threevolt rechargeable battery 139 sits within the cam barrel 125 in contactwith the battery contacts. An induction charging coil 140 is mountedabout the second flex PCB 129 to enable recharging of the battery 139via induction. The second flex PCB 129 also mounts an infrared LED 143and infrared photodiode 144 for detecting displacement in the cam barrel125 when either the stylus 120 or the ink cartridge 118 is used forwriting, in order to enable a determination of the force being appliedto the surface by the pen nib 119 or stylus nib 121. The IR photodiode144 detects light from the IR LED 143 via reflectors (not shown) mountedon the slider blocks 123 and 124.

Rubber grip pads 141 and 142 are provided towards the end 108 of thehousing 102 to assist gripping the pen 101, and top 105 also includes aclip 142 for clipping the pen 101 to a pocket.

6.2 Pen Controller

The pen 101 is arranged to determine the position of its nib (stylus nib121 or ink cartridge nib 119) by imaging, in the infrared spectrum, anarea of the surface in the vicinity of the nib. It records the locationdata from the nearest location tag, and is arranged to calculate thedistance of the nib 121 or 119 from the location tab utilising optics135 and controller chip 134. The controller chip 134 calculates theorientation of the pen and the nib-to-tag distance from the perspectivedistortion observed on the imaged tag.

Utilising the RF chip 133 and antenna 112 the pen 101 can transmit thedigital ink data (which is encrypted for security and packaged forefficient transmission) to the computing system.

When the pen is in range of a receiver, the digital ink data istransmitted as it is formed. When the pen 101 moves out of range,digital ink data is buffered within the pen 101 (the pen 101 circuitryincludes a buffer arranged to store digital ink data for approximately12 minutes of the pen motion on the surface) and can be transmittedlater.

The controller chip 134 is mounted on the second flex PCB 129 in the pen101. FIG. 10 is a block diagram illustrating in more detail thearchitecture of the controller chip 134. FIG. 10 also showsrepresentations of the RF chip 133, the image sensor 132, the tri-colorstatus LED 116, the IR illumination LED 131, the IR force sensor LED143, and the force sensor photodiode 144.

The pen controller chip 134 includes a controlling processor 145. Bus146 enables the exchange of data between components of the controllerchip 134. Flash memory 147 and a 512 KB DRAM 148 are also included. Ananalog-to-digital converter 149 is arranged to convert the analog signalfrom the force sensor photodiode 144 to a digital signal.

An image sensor interface 152 interfaces with the image sensor 132. Atransceiver controller 153 and base band circuit 154 are also includedto interface with the RF chip 133 which includes an RF circuit 155 andRF resonators and inductors 156 connected to the antenna 112.

The controlling processor 145 captures and decodes location data fromtags from the surface via the image sensor 132, monitors the forcesensor photodiode 144, controls the LEDs 116, 131 and 143, and handlesshort-range radio communication via the radio transceiver 153. It is amedium-performance (−40 MHz) general-purpose RISC processor. Theprocessor 145, digital transceiver components (transceiver controller153 and baseband circuit 154), image sensor interface 152, flash memory147 and 512 KB DRAM 148 are integrated in a single controller ASIC.Analog RF components (RF circuit 155 and RF resonators and inductors156) are provided in the separate RF chip.

The image sensor is a 215×215 pixel CCD (such a sensor is produced byMatsushita Electronic Corporation, and is described in a paper byItakura, K T Nobusada, N Okusenya, R Nagayoshi, and M Ozaki, “A 1 mm 50k-Pixel IT CCD Image Sensor for Miniature Camera System”, IEEETransactions on Electronic Devices, Volt 47, number 1, January 2000,which is incorporated herein by reference) with an IR filter.

The controller ASIC 134 enters a quiescent state after a period ofinactivity when the pen 101 is not in contact with a surface. Itincorporates a dedicated circuit 150 which monitors the force sensorphotodiode 144 and wakes up the controller 134 via the power manager 151on a pen-down event.

The radio transceiver communicates in the unlicensed 900 MHz bandnormally used by cordless telephones, or alternatively in the unlicensed2.4 GHz industrial, scientific and medical (ISM) band, and usesfrequency hopping and collision detection to provide interference-freecommunication.

In an alternative embodiment, the pen incorporates an Infrared DataAssociation (IrDA) interface for short-range communication with a basestation or netpage printer.

In a further embodiment, the pen 101 includes a pair of orthogonalaccelerometers mounted in the normal plane of the pen 101 axis. Theaccelerometers 190 are shown in FIGS. 9 and 10 in ghost outline.

The provision of the accelerometers enables this embodiment of the pen101 to sense motion without reference to surface location tags, allowingthe location tags to be sampled at a lower rate. Each location tag IDcan then identify an object of interest rather than a position on thesurface. For example, if the object is a user interface input element(e.g. a command button), then the tag ID of each location tag within thearea of the input element can directly identify the input element.

The acceleration measured by the accelerometers in each of the x and ydirections is integrated with respect to time to produce aninstantaneous velocity and position.

Since the starting position of the stroke is not known, only relativepositions within a stroke are calculated. Although position integrationaccumulates errors in the sensed acceleration, accelerometers typicallyhave high resolution, and the time duration of a stroke, over whicherrors accumulate, is short.

7. Netpage Printer Description

7.1 Printer Mechanics

The vertically-mounted netpage wallprinter 601 is shown fully assembledin FIG. 11. It prints netpages on Letter/A4 sized media using duplexed8½″ Memjet™ print engines 602 and 603, as shown in FIGS. 12 and 12 a. Ituses a straight paper path with the paper 604 passing through theduplexed print engines 602 and 603 which print both sides of a sheetsimultaneously, in full color and with full bleed.

An integral binding assembly 605 applies a strip of glue along one edgeof each printed sheet, allowing it to adhere to the previous sheet whenpressed against it. This creates a final bound document 618 which canrange in thickness from one sheet to several hundred sheets.

The replaceable ink cartridge 627, shown in FIG. 13 coupled with theduplexed print engines, has bladders or chambers for storing fixative,adhesive, and cyan, magenta, yellow, black and infrared inks. Thecartridge also contains a micro air filter in a base molding. The microair filter interfaces with an air pump 638 inside the printer via a hose639. This provides filtered air to the printheads to preventingress ofmicro particles into the Memjet™ printheads 350 which might otherwiseclog the printhead nozzles. By incorporating the air filter within thecartridge, the operational life of the filter is effectively linked tothe life of the cartridge. The ink cartridge is a fully recyclableproduct with a capacity for printing and gluing 3000 pages (1500sheets).

Referring to FIG. 12, the motorized media pick-up roller assembly 626pushes the top sheet directly from the media tray past a paper sensor onthe first print engine 602 into the duplexed Memjet™ printhead assembly.The two Memjet™ print engines 602 and 603 are mounted in an opposingin-line sequential configuration along the straight paper path. Thepaper 604 is drawn into the first print engine 602 by integral, poweredpick-up rollers 626. The position and size of the paper 604 is sensedand full bleed printing commences. Fixative is printed simultaneously toaid drying in the shortest possible time.

The paper exits the first Memjet™ print engine 602 through a set ofpowered exit spike wheels (aligned along the straight paper path), whichact against a rubberized roller. These spike wheels contact the ‘wet’printed surface and continue to feed the sheet 604 into the secondMemjet™ print engine 603.

Referring to FIGS. 12 and 12 a, the paper 604 passes from the duplexedprint engines 602 and 603 into the binder assembly 605. The printed pagepasses between a powered spike wheel axle 670 with a fibrous supportroller and another movable axle with spike wheels and a momentary actionglue wheel. The movable axle/glue assembly 673 is mounted to a metalsupport bracket and it is transported forward to interface with thepowered axle 670 via gears by action of a camshaft. A separate motorpowers this camshaft.

The glue wheel assembly 673 consists of a partially hollow axle 679 witha rotating coupling for the glue supply hose 641 from the ink cartridge627. This axle 679 connects to a glue wheel, which absorbs adhesive bycapillary action through radial holes. A molded housing 682 surroundsthe glue wheel, with an opening at the front. Pivoting side moldings andsprung outer doors are attached to the metal bracket and hinge outsideways when the rest of the assembly 673 is thrust forward. Thisaction exposes the glue wheel through the front of the molded housing682. Tension springs close the assembly and effectively cap the gluewheel during periods of inactivity.

As the sheet 604 passes into the glue wheel assembly 673, adhesive isapplied to one vertical edge on the front side (apart from the firstsheet of a document) as it is transported down into the binding assembly605.

7.2 Printer Controller Architecture

The netpage printer controller consists of a controlling processor 750,a factory-installed or field-installed network interface module 625, aradio transceiver (transceiver controller 753, baseband circuit 754, RFcircuit 755, and RF resonators and inductors 756), dual raster imageprocessor (RIP) DSPs 757, duplexed print engine controllers 760 a and760 b, flash memory 658, and 64 MB of DRAM 657, as illustrated in FIG.14.

The controlling processor handles communication with the network 19 andwith local wireless netpage pens 101, senses the help button 617,controls the user interface LEDs 613-616, and feeds and synchronizes theRIP DSPs 757 and print engine controllers 760. It consists of amedium-performance general-purpose microprocessor. The controllingprocessor 750 communicates with the print engine controllers 760 via ahigh-speed serial bus 659.

The RIP DSPs rasterize and compress page descriptions to the netpageprinter's compressed page format. Each print engine controller expands,dithers and prints page images to its associated Memjet™ printhead 350in real time (i.e. at over 30 pages per minute). The duplexed printengine controllers print both sides of a sheet simultaneously. Themaster print engine controller 760 a controls the paper transport andmonitors ink usage in conjunction with the master QA chip 665 and theink cartridge QA chip 761.

The printer controller's flash memory 658 holds the software for boththe processor 750 and the DSPs 757, as well as configuration data. Thisis copied to main memory 657 at boot time.

The processor 750, DSPs 757, and digital transceiver components(transceiver controller 753 and baseband circuit 754) are integrated ina single controller ASIC 656. Analog RF components (RF circuit 755 andRF resonators and inductors 756) are provided in a separate RF chip 762.The network interface module 625 is separate, since netpage printersallow the network connection to be factory-selected or field-selected.Flash memory 658 and the 2×256 Mbit (64 MB) DRAM 657 is also off-chip.The print engine controllers 760 are provided in separate ASICs.

A variety of network interface modules 625 are provided, each providinga netpage network interface 751 and optionally a local computer ornetwork interface 752. Netpage network Internet interfaces include POTSmodems, Hybrid Fiber-Coax (HFC) cable modems, ISDN modems, DSL modems,satellite transceivers, current and next-generation cellular telephonetransceivers, and wireless local loop (WLL) transceivers. Localinterfaces include IEEE 1284 (parallel port), 10Base-T and 100Base-TEthernet, USB and USB 2.0, IEEE 1394 (Firewire), and various emerginghome networking interfaces. If an Internet connection is available onthe local network, then the local network interface can be used as thenetpage network interface.

The radio transceiver 753 communicates in the unlicensed 900 MHz bandnormally used by cordless telephones, or alternatively in the unlicensed2.4 GHz industrial, scientific and medical (ISM) band, and usesfrequency hopping and collision detection to provide interference-freecommunication.

The printer controller optionally incorporates an Infrared DataAssociation (IrDA) interface for receiving data “squirted” from devicessuch as netpage cameras. In an alternative embodiment, the printer usesthe IrDA interface for short-range communication with suitablyconfigured netpage pens.

7.2.1 Rasterization and Printing

Once the main processor 750 has received and verified the document'spage layouts and page objects, it runs the appropriate RIP software onthe DSPs 757.

The DSPs 757 rasterize each page description and compress the rasterizedpage image. The main processor stores each compressed page image inmemory. The simplest way to load-balance multiple DSPs is to let eachDSP rasterize a separate page. The DSPs can always be kept busy since anarbitrary number of rasterized pages can, in general, be stored inmemory. This strategy only leads to potentially poor DSP utilizationwhen rasterizing short documents.

Watermark regions in the page description are rasterized to acontone-resolution bi-level bitmap which is losslessly compressed tonegligible size and which forms part of the compressed page image.

The infrared (IR) layer of the printed page contains coded netpage tagsat a density of about six per inch. Each tag encodes the page ID, tagID, and control bits, and the data content of each tag is generatedduring rasterization and stored in the compressed page image.

The main processor 750 passes back-to-back page images to the duplexedprint engine controllers 760. Each print engine controller 760 storesthe compressed page image in its local memory, and starts the pageexpansion and printing pipeline. Page expansion and printing ispipelined because it is impractical to store an entire 114 MB bi-levelCMYK-FIR page image in memory.

7.2.2 Print Engine Controller

The page expansion and printing pipeline of the print engine controller760 consists of a high speed IEEE 1394 serial interface 659, a standardJPEG decoder 763, a standard Group 4 Fax decoder 764, a customhalftoner/compositor unit 765, a custom tag encoder 766, a lineloader/formatter unit 767, and a custom interface 768 to the Memjet™printhead 350.

The print engine controller 360 operates in a double buffered manner.While one page is loaded into DRAM 769 via the high speed serialinterface 659, the previously loaded page is read from DRAM 769 andpassed through the print engine controller pipeline. Once the page hasfinished printing, the page just loaded is printed while another page isloaded.

The first stage of the pipeline expands (at 763) the JPEG-compressedcontone CMYK layer, expands (at 764) the Group 4 Fax-compressed bi-levelblack layer, and renders (at 766) the bi-level netpage tag layeraccording to the tag format defined in section 1.2, all in parallel. Thesecond stage dithers (at 765) the contone CMYK layer and composites (at765) the bi-level black layer over the resulting bi-level CMYK layer.The resultant bi-level CMYK-FIR dot data is buffered and formatted (at767) for printing on the Memjet™ printhead 350 via a set of linebuffers. Most of these line buffers are stored in the off-chip DRAM. Thefinal stage prints the six channels of bi-level dot data (includingfixative) to the Memjet™ printhead 350 via the printhead interface 768.

When several print engine controllers 760 are used in unison, such as ina duplexed configuration, they are synchronized via a shared line syncsignal 770. Only one print engine 760, selected via the externalmaster/slave pin 771, generates the line sync signal 770 onto the sharedline.

The print engine controller 760 contains a low-speed processor 772 forsynchronizing the page expansion and rendering pipeline, configuring theprinthead 350 via a low-speed serial bus 773, and controlling thestepper motors 675, 676.

In the 8½″ versions of the netpage printer, the two print engines eachprints 30 Letter pages per minute along the long dimension of the page(11″), giving a line rate of 8.8 kHz at 1600 dpi. In the 12″ versions ofthe netpage printer, the two print engines each prints 45 Letter pagesper minute along the short dimension of the page (8½″), giving a linerate of 10.2 kHz. These line rates are well within the operatingfrequency of the Memjet™ printhead, which in the current design exceeds30 kHz.

8. Print Engine Controller and Tag Encoder

A typically 12 inch printhead width is controlled by one or more PECs,as described below, to allow full-bleed printing of both A4 and Letterpages. Six channels of colored ink are the expected maximum in thepresent printing environment, these being:

-   -   CMY, for regular color printing.    -   K, for black text and other black printing.    -   IR (infrared), for Netpage-enabled applications.    -   F (fixative), to enable printing at high speed.

Because the printer is to be capable of fast printing, a fixative willbe required to enable the ink to dry before the next page has completedprinting at higher speeds. Otherwise the pages might bleed on eachother. In lower speed printing environments the fixative will not be notrequired. A PEC might be built in a single chip to interface with aprinthead. It will contain four basic levels of functionality:

-   -   receiving compressed pages via a serial interface such as IEEE        1394    -   a print engine for producing a page from a compressed form. The        print engine functionality includes expanding the page image,        dithering the contone layer, compositing the black layer over        the contone layer, and sending the resultant image to the        printhead.    -   a print controller for controlling the printhead and stepper        motors.    -   two standard low-speed serial ports for communication with the        two QA chips. Note that there must be two ports and not a single        port to ensure strong security during the authentication        procedure.

In FIG. 48 is seen the flow of data to send a document from computersystem to printed page. A document is received at 411 and loaded tomemory buffer 412 wherein page layouts may be effected and any requiredobjects might be added. Pages from memory 412 are rasterized at 413 andcompressed at 414 prior to transmission to the print engine controller410. Pages are received as compressed two-layer page images within theprint engine controller 410 into a memory buffer 415, from which theyare fed to a page expander 416 wherein page images are retrieved. Anyrequisite dither might be applied to any contone layer at 417. Any blackbi-level layer might be composited over the contone layer at 418together with any infrared tags at 419. The composited page data isprinted at 420 to produce page 421.

The print engine/controller takes the compressed page image and startsthe page expansion and printing in pipeline fashion. Page expansion andprinting is preferably pipelined because it is impractical to store asizable bi-level CMYK-FIR page image in memory.

The first stage of the pipeline expands a JPEG-compressed contone CMYKlayer (see below), expands a Group 4 Fax-compressed bi-level dithermatrix selection map (see below), and expands a Group 4 Fax-compressedbi-level black layer (see below), all in parallel. The second stagedithers the contone CMYK layer using a dither matrix selected by thedither matrix select map, and composites the bi-level black layer overthe resulting bi-level K layer. In parallel with this, the tag encoderencodes bi-level IR tag data from the compressed page image. A fixativelayer is also generated at each dot position wherever there is a need inany of C, M, Y, K, or IR channels. The last stage prints the bi-levelCMYK+IR data through the printhead via a printhead interface (seebelow).

In FIG. 49 is seen how the print engine/controller 410 fits within theoverall printer system architecture. The various components of theprinter system might include

-   -   a Print Engine/Controller (PEC). A PEC chip 410, or chips, is        responsible for receiving the compressed page images for storage        in a memory buffer 424, performing the page expansion, black        layer compositing and sending the dot data to the printhead 423.        It may also communicate with QA chips 425, 426 and provides a        means of retrieving printhead characteristics to ensure optimum        printing. The PEC is the subject of this specification.    -   a memory buffer. The memory buffer 424 is for storing the        compressed page image and for scratch use during the printing of        a given page. The construction and working of memory buffers is        known to those skilled in the art and a range of standard chips        and techniques for their use might be utilised in use of the PEC        of the invention.    -   a master QA chip. The master chip 425 is matched to replaceable        ink cartridge QA chips 426. The construction and working of QA        units is known to those skilled in the art and a range of known        QA processes might be utilised in use of the PEC of the        invention. For example, a QA chip is described in co-pending        United States Patent Applications:

U.S. Ser. No. Our Title 7,249,108 Validation Protocol and System6,566,858 Circuit for Protecting Chips Against IDD Fluctuation Attacks6,331,946 Method for Protecting On-Chip Memory (Flash and RAM) 6,246,970Method for Making a Chip Tamper-Resistant 6,442,525 A system forauthenticating physical objects 7,346,586 Validation Protocol and System09/505,951 Validation Protocol and System 6,374,354 ConsumableAuthentication Protocol and System 7,246,098 Consumable AuthenticationProtocol and System 6,816,968 Consumable Authentication Protocol andSystem 6,757,832 Unauthorized Modification of Values Stored in FlashMemory 6,334,190 A System for the Manipulation of Secure Data 6,745,331An Authentication Chip with Protection from Power Supply Attacks7,249,109 Shielding Manipulations of Secret Data

QA chip communication may be best included within the overallfunctionality of the PEC chip since it has a role in the expansion ofthe image as well as running the physical printhead. By locating QA chipcommunication there it can be ensured that there is enough ink to printthe page. Preferably the QA embedded in the printhead assembly isimplemented using an authentication chip. Since it is a master QA chip,it only contains authentication keys, and does not contain user-data.However, it must match the ink cartridge's QA chip. The QA chip in theink cartridge contains information required for maintaining the bestpossible print quality, and is implemented using an authentication chip.

Preferably a 64 MBit (8 MByte) memory buffer is used to store thecompressed page image. While one page is being written to the bufferanother is being read (double buffering). In addition, the PEC uses thememory to buffer the calculated dot information during the printing of apage. During the printing of page N, the buffer is used for:

-   -   Reading compressed page N    -   Reading and writing the bi-level dot information for page N    -   Writing compressed page N+1

Preferably a PEC chip will incorporate a simple micro-controller CPUcore 435 to perform the following functions:

-   -   perform QA chip authentication protocols between print pages    -   run the stepper motor at parallel interface 589 during a print        (the stepper motor requires a 5 KHz process)    -   synchronize the various portions of the PEC chip during a print    -   provide a means of interfacing with external data requests        (programming registers etc.)    -   provide a means of interfacing with printhead segment low-speed        data requests (such as reading the characterization vectors and        writing pulse profiles)    -   provide a means of writing the portrait and landscape tag        structures to external DRAM

Since all of the image processing is performed by dedicated hardware,the CPU does not have to process pixels. As a result, the CPU can beextremely simple. A wide variety of CPU known cores are suitable: it canbe any processor core with sufficient processing power to perform therequired calculations and control functions fast enough. An example of asuitable core is a Philips 8051 micro-controller running at about 1 MHz.Associated with the CPU core 435 may be a program ROM and a smallprogram scratch RAM. The CPU communicates with the other units withinthe PEC chip via memory-mapped I/O. Particular address ranges may map toparticular units, and within each range, to particular registers withinthat particular unit. This includes the serial and parallel interfaces.A small program flash ROM may be incorporated into the PEC chip. Itssize depends on the CPU chosen, but should not be more than 8 KB.Likewise, a small scratch RAM area can be incorporated into the PECchip. Since the program code does not have to manipulate images, thereis no need for a large scratch area. The RAM size depends on the CPUchosen (e.g. stack mechanisms, subroutine calling conventions, registersizes etc.), but should not be more than about 2 KB.

A PEC chip using the above referenced segment based page wide printheadcan reproduce black at a full dot resolution (typically 1600 dpi), butreproduces contone color at a somewhat lower resolution usinghalftoning. The page description is therefore divided into a blackbi-level layer and a contone layer. The black bi-level layer is definedto composite over the contone layer. The black bi-level layer consistsof a bitmap containing a 1-bit opacity for each pixel. This black layermatte has a resolution which is an integer factor of the printer's dotresolution. The highest supported resolution is 1600 dpi, i.e. theprinter's full dot resolution. The contone layer consists of a bitmapcontaining a 32-bit CMYK color for each pixel, where K is optional. Thiscontone image has a resolution which is an integer factor of theprinter's dot resolution. The highest supported resolution is 320 ppiover 12 inches for a single PEC, i.e. one-fifth the printer's dotresolution. For higher contone resolutions multiple PECs are required,with each PEC producing an strip of the output page. The contoneresolution is also typically an integer factor of the black bi-levelresolution, to simplify calculations in the RIPs. This is not arequirement, however. The black bi-level layer and the contone layer areboth in compressed form for efficient storage in the printer's internalmemory.

In FIG. 50 is seen the print engine architecture. The print engine'spage expansion and printing pipeline consists of a high speed serialinterface 427 (such as a standard IEEE 1394 interface), a standard JPEGdecoder 428, a standard Group 4 Fax decoder, a customhalftoner/compositor unit 429, a custom tag encoder 430, a lineloader/formatter unit 431, and a custom interface 432 to the printhead433. The decoders 428, 588 and encoder 430 are buffered to thehalftoner/compositor 429.

The tag encoder 430 establishes an infrared tag or tags to a pageaccording to protocols dependent on what uses might be made of the pageand the actual content of a tag is not the subject of the presentinvention.

The print engine works in a double buffered way. One page is loaded intoDRAM 34 via a DRAM interface 587 on bus 586 and the high speed serialinterface 27 while the previously loaded page is read from DRAM 434 andpassed through the print engine pipeline. Once the page has finishedprinting, then the page just loaded becomes the page being printed, anda new page is loaded via the high speed serial interface 427. At thefirst stage the pipeline expands any JPEG-compressed contone (CMYK)layer, and expands any of two Group 4 Fax-compressed bi-level datastreams. The two streams are the black layer (although the PEC isactually color agnostic and this bi-level layer can be directed to anyof the output inks), and a matte for selecting between dither matricesfor contone dithering (see below). At the second stage, in parallel withthe first, is encoded any tags for later rendering in either IR or blackink. Finally the third stage dithers the contone layer, and compositesposition tags and the bi-level spot1 layer over the resulting bi-leveldithered layer. The datastream is ideally adjusted to create smoothtransitions across overlapping segments in the printhead and ideally itis adjusted to compensate for dead nozzles in the printhead. Up to 6channels of bi-level data are produced from this stage. Note that notall 6 channels may be present on the printhead. For example, theprinthead may be CMY only, with K pushed into the CMY channels and IRignored. Alternatively, the position tags may be printed in K if IR inkis not available (or for testing purposes). The resultant bi-levelCMYK-IR dot-data is buffered and formatted for printing on the printhead33 via a set of line buffers (see below). The majority of these linebuffers might be ideally stored on the off-chip DRAM 434. The finalstage prints the 6 channels of bi-level dot data via the printheadinterface 432.

Compression is used in a printing system that employs the PEC. This isto enable the data flow to keep ahead of the printhead that is run at aconstant speed. At 267 ppi, a Letter page of contone CMYK data has asize of 25 MB. Using lossy contone compression algorithms such as JPEG(see below), contone images compress with a ratio up to 10:1 withoutnoticeable loss of quality, giving a compressed page size of 2.5 MB. At800 dpi, a Letter page of bi-level data has a size of 7 MB. Coherentdata such as text compresses very well. Using lossless bi-levelcompression algorithms such as Group 4 Facsimile (see below), ten-pointtext compresses with a ratio of about 10:1, giving a compressed pagesize of 0.8 MB. Once dithered, a page of CMYK contone image dataconsists of 114 MB of bi-level data. The two-layer compressed page imageformat described below exploits the relative strengths of lossy JPEGcontone image compression and lossless bi-level text compression. Theformat is compact enough to be storage-efficient, and simple enough toallow straightforward real-time expansion during printing. Since textand images normally don't overlap, the normal worst-case page image sizeis 2.5 MB (i.e. image only), while the normal best-case page image sizeis 0.8 MB (i.e. text only). The absolute worst-case page image size is3.3 MB (i.e. text over image). Assuming a quarter of an average pagecontains images, the average page image size is 1.2 MB.

The Group 4 Fax (G4 Fax) decoder is responsible for decompressingbi-level data. Bi-level data is limited to a single spot color(typically black for text and line graphics), and a dither matrix selectbit-map for use in subsequent dithering of the contone data(decompressed by the JPEG decoder). The input to the G4 Fax decoder is 2planes of bi-level data, read from the external DRAM. The output of theG4 Fax decoder is 2 planes of decompressed bi-level data. Thedecompressed bi-level data is sent to the Halftoner/Compositor Unit(HCU) for the next stage in the printing pipeline. Two bi-level buffersprovides the means for transferring the bi-level data between the G4 Faxdecoder and the HCU. Each decompressed bi-level layer is output to twoline buffers. Each buffer is capable of holding a full 12 inch line ofdots at the expected maximum resolution. Having two line buffers allowsone line to be read by the HCU while the other line is being written toby the G4 Fax decoder. This is important because a single bi-level lineis typically less than 1600 dpi, and must therefore be expanded in boththe dot and line dimensions. If the buffering were less than a fullline, the G4 Fax decoder would have to decode the same line multipletimes—once for each output 600 dpi dotline.

Spot color 1 is designed to allow high resolution dot data for a singlecolor plane of the output image. While the contone layers provideadequate resolution for images, spot color 1 is targeted at applicationssuch as text and line graphics (typically black). When used as text andline graphics, the typical compression ratio exceeds 10:1. Spot color 1allows variable resolution up to 1600 dpi for maximum print quality.Each of the two line buffers is therefore total 2400 bytes (12inches×1600 dpi=19,200 bits).

The resolution of the dither matrix select map should ideally match thecontone resolution. Consequently each of the two line buffers istherefore 480 bytes (3840 bits), capable of storing 12 inches at 320dpi. When the map matches the contone resolution, the typicalcompression ratio exceeds 50:1.

In order to provide support for:

-   -   800 dpi spot color 1 layer (typically black)    -   320 dpi dither matrix select layer        the decompression bandwidth requirements are 9.05 MB/sec for 1        page per second performance (regardless of whether the page        width is 12 inches or 8.5 inches), and 20 MB/sec and 14.2 MB/sec        for 12 inch and 8.5 inch page widths respectively during maximum        printer speed performance (30,000 lines per second). Given that        the decompressed data is output to a line buffer, the G4 Fax        decoder can readily decompress a line from each of the outputs        one at a time. The G4 Fax decoder is fed directly from the main        memory via the DRAM interface. The amount of compression        determines the bandwidth requirements to the external DRAM.        Since G4 Fax is lossless, the complexity of the image impacts on        the amount of data and hence the bandwidth. typically an 800 dpi        black text/graphics layer exceeds 10:1 compression, so the        bandwidth required to print 1 page per second is 0.78 MB/sec.        Similarly, a typical 320 dpi dither select matrix compresses at        more than 50:1, resulting in a 0.025 MB/sec bandwidth. The        fastest printing speed configuration of 320 dpi for dither        select matrix and 800 dpi for spot color 1 requires bandwidth of        1.72 MB/sec and 0.056 MB/sec respectively. A total bandwidth of        2 MB/sec should therefore be more than enough for the DRAM        bandwidth.

The G4 Fax decoding functionality is implemented by means of a G4 FaxDecoder core. A wide variety of G4Fax Decoder cores are suitable: it canbe any core with sufficient processing power to perform the requiredcalculations and control functions fast enough. It must be capable ofhandling runlengths exceeding those normally encountered in 400 dpifacsimile applications, and so may require modification.

The CMYK (or CMY) contone layer is compressed to a planar color JPEGbytestream. If luminance/chrominance separation is deemed necessary,either for the purposes of table sharing or for chrominance subsampling,then CMYK is converted to YCrCb and Cr and Cb are duly subsampled. TheJPEG bytestream is complete and self-contained. It contains all datarequired for decompression, including quantization and Huffman tables.

The JPEG decoder is responsible for performing the on-the-flydecompression of the contone data layer. The input to the JPEG decoderis up to 4 planes of contone data. This will typically be 3 planes,representing a CMY contone image, or 4 planes representing a CMYKcontone image. Each color plane can be in a different resolution,although typically all color planes will be the same resolution. Thecontone layers are read from the external DRAM. The output of the JPEGdecoder is the decompressed contone data, separated into planes. Thedecompressed contone image is sent to the halftoner/compositor unit(HCU) 429 for the next stage in the printing pipeline. The 4-planecontone buffer provides the means for transferring the contone databetween the JPEG decoder and the HCU 429.

Each color plane of the decompressed contone data is output to a set oftwo line buffers (see below). Each line buffer is 3840 bytes, and istherefore capable of holding 12 inches of a single color plane's pixelsat 320 ppi. The line buffering allows one line buffer to be read by theHCU while the other line buffer is being written to by the JPEG decoder.This is important because a single contone line is typically less than1600 ppi, and must therefore be expanded in both the dot and linedimensions. If the buffering were less than a full line, the JPEGdecoder would have to decode the same line multiple times—once for eachoutput 600 dpi dotline. Although a variety of resolutions is supported,there is a tradeoff between the resolution and available bandwidth. Asresolution and number of colors increase, bandwidth requirements alsoincrease. In addition, the number of segments being targeted by the PECchip also affects the bandwidth and possible resolutions. Note thatsince the contone image is processed in a planar format, each colorplane can be stored at a different resolution (for example CMY may be ahigher resolution than the K plane). The highest supported contoneresolution is 1600 ppi (matching the printer's full dot resolution).However there is only enough output line buffer memory to hold enoughcontone pixels for a 320 ppi line of length 12 inches. If the full 12inches of output was required at higher contone resolution, multiple PECchips would be required, although it should be noted that the finaloutput on the printer will still only be bi-level. With support for 4colors at 320 ppi, the decompression output bandwidth requirements are40 MB/sec for 1 page per second performance (regardless of whether thepage width is 12 inches or 8.5 inches), and 88 MB/sec and 64 MB/sec for12 inch and 8.5 inch page widths respectively during maximum printerspeed performance (30,000 lines per second). Table 5 can be used todetermine the bandwidth required for different resolution/colorplane/page width combinations.

The JPEG decoder is fed directly from the main memory via the DRAMinterface. The amount of compression determines the bandwidthrequirements to the external DRAM. As the level of compressionincreases, the bandwidth decreases, but the quality of the final outputimage can also decrease. The DRAM bandwidth for a single color plane canbe readily calculated by applying the compression factor to the outputbandwidth shown in Table 5. For example, a single color plane at 320 ppiwith a compression factor of 10:1 requires 1 MB/sec access to DRAM toproduce a single page per second.

The JPEG functionality is implemented by means of a JPEG core. A widevariety of JPEG cores are suitable: it can be any JPEG core withsufficient processing power to perform the required calculations andcontrol functions fast enough. For example, the BTG X-Match core hasdecompression speeds up to 140 MBytes/sec, which allows decompression of4 color planes at contone resolutions up to 400 ppi for the maximumprinter speed (30,000 lines at 1600 dpi per second), and 800 ppi for 1page/sec printer speed. Note that the core needs to only supportdecompression, reducing the requirements that are imposed by moregeneralized JPEG compression/decompression cores. The size of the coreis expected to be no more than 100,000 gates. Given that thedecompressed data is output to a line buffer, the JPEG decoder canreadily decompress an entire line for each of the color planes one at atime, thus saving on context switching during a line and simplifying thecontrol of the JPEG decoder. 4 contexts must be kept (1 context for eachcolor plane), and includes current address in the external DRAM as wellas appropriate JPEG decoding parameters

In FIG. 51 the halftoner/compositor unit (HCU) 429 combines thefunctions of halftoning the contone (typically CMYK) layer to a bi-levelversion of the same, and compositing the spot1 bi-level layer over theappropriate halftoned contone layer(s). If there is no K ink in theprinter, the HCU 429 is able to map K to CMY dots as appropriate. Italso selects between two dither matrices on a pixel by pixel basis,based on the corresponding value in the dither matrix select map. Theinput to the HCU 429 is an expanded contone layer (from the JPEG decoderunit) through buffer 437, an expanded bi-level spot1 layer throughbuffer 438, an expanded dither-matrix-select bitmap at typically thesame resolution as the contone layer through buffer 439, and tag data atfull dot resolution through buffer 440. The HCU 429 uses up to twodither matrices, read from the external DRAM 434. The output from theHCU 429 to the line loader/format unit (LLFU) at 441 is a set of printerresolution bi-level image lines in up to 6 color planes. Typically, thecontone layer is CMYK or CMY, and the bi-level spot1 layer is K.

In FIG. 52 is seen the HCU in greater detail. Once started, the HCUproceeds until it detects an end-of-page condition, or until it isexplicitly stopped via its control register. The first task of the HCUis to scale, in the respective scale units such as the scale unit 443,all data, received in the buffer planes such as 442, to printerresolution both horizontally and vertically. The scale unit provides ameans of scaling contone or bi-level data to printer resolution bothhorizontally and vertically. Scaling is achieved by replicating a datavalue an integer number of times in both dimensions. Processes by whichto scale data will be familiar to those skilled in the art. Since eachof the contone layers can be a different resolution, they are scaledindependently. The bi-level spot1 layer at buffer 445 and the dithermatrix select layer at buffer 446 also need to be scaled. The bi-leveltag data at buffer 447 is established at the correct resolution and doesnot need to be scaled. The scaled-up dither matrix select bit is used bythe dither matrix access unit 448 to select a single 8-bit value fromthe two dither matrices. The 8-bit value is output to the 4 comparators444, and 449 to 451, which simply compare it to the specific 8-bitcontone value. The generation of an actual dither matrix is dependent onthe structure of the printhead and the general processes by which togenerate one will be familiar to those skilled in the art. If thecontone value is greater than or equal to the 8-bit dither matrix valuea 1 is output. If not, then a 0 is output. These bits are then all ANDedat 452 to 456 with an in Page bit from the margin unit 457 (whether ornot the particular dot is inside the printable area of the page). Thefinal stage in the HCU is the compositing stage. For each of the 6output layers there is a single dot merger unit, such as unit 458, eachwith 6 inputs. The single output bit from each dot merger unit is acombination of any or all of the input bits. This allows the spot colorto be placed in any output color plane (including infrared for testingpurposes), black to be merged into cyan, magenta and yellow (if no blackink is present in the printhead), and tag dot data to be placed in avisible plane. A fixative color plane can also be readily generated. Thedot reorg unit (DRU) 459 is responsible for taking the generated dotstream for a given color plane and organizing it into 32-bit quantitiesso that the output is in segment order, and in dot order withinsegments. Minimal reordering is required due to the fact that dots foroverlapping segments are not generated in segment order.

Two control bits are provided to the scale units by the margin unit 457:advance dot and advance line. The advance dot bit allows the statemachine to generate multiple instances of the same dot data (useful forpage margins and creating dot data for overlapping segments in theMemjet printhead). The advance line bit allows the state machine tocontrol when a particular line of dots has been finished, therebyallowing truncation of data according to printer margins. It also savesthe scale unit from requiring special end-of-line logic.

The comparator unit contains a simple 8-bit “greater-than-or-equal”comparator. It is used to determine whether the 8-bit contone value isgreater than or equal to the 8-bit dither matrix value. As such, thecomparator unit takes two 8-bit inputs and produces a single 1-bitoutput.

In FIG. 53 is seen more detail of the dot merger unit. It provides ameans of mapping the bi-level dithered data, the spot1 color, and thetag data to output inks in the actual printhead. Each dot merger unittakes 6 1-bit inputs and produces a single bit output that representsthe output dot for that color plane. The output bit at 460 is acombination of any or all of the input bits. This allows the spot colorto be placed in any output color plane (including infrared for testingpurposes), black to be merged into cyan, magenta and yellow (in the caseof no black ink in the printhead), and tag dot data to be placed in avisible plane. An output for fixative can readily be generated by simplycombining all of the input bits. The dot merger unit contains a 6-bitColorMask register 461 that is used as a mask against the 6 input bits.Each of the input bits is ANDed with the corresponding ColorMaskregister bit, and the resultant 6 bits are then ORed together to formthe final output bit.

In FIG. 54 is seen the dot reorg unit (DRU) which is responsible fortaking the generated dot stream for a given color plane and organizingit into 32-bit quantities so that the output is in segment order, and indot order within segments. Minimal reordering is required due to thefact that dots for overlapping segments are not generated in segmentorder. The DRU contains a 32-bit shift register, a regular 32-bitregister, and a regular 16-bit register. A 5-bit counter keeps track ofthe number of bits processed so far. The dot advance signal from thedither matrix access unit (DMAU) is used to instruct the DRU as to whichbits should be output.

In FIG. 54 register(A) 462 is clocked every cycle. It contains the 32most recent dots produced by the dot merger unit (DMU). The full 32-bitvalue is copied to register(B) 463 every 32 cycles by means of aWriteEnable signal produced by the DRU state machine 464 via a simple5-bit counter. The 16 odd bits (bits 1, 3, 5, 7 etc.) from register(B)463 are copied to register(C) 465 with the same WriteEnable pulse. A32-bit multiplexor 466 then selects between the following 3 outputsbased upon 2 bits from the state machine:

The full 32 bits from register B

-   -   A 32-bit value made up from the 16 even bits of register A (bits        0, 2, 4, 6 etc.) and the 16 even bits of register B. The 16 even        bits from register A form bits 0 to 15, while the 16 even bits        from register B form bits 16-31.    -   A 32-bit value made up from the 16 odd bits of register B (bits        1, 3, 5, 7 etc.) and the 16 bits of register C. The bits of        register C form bits 0 to 15, while the odd bits from register B        form bits 16-31.

The state machine for the DRU can be seen in Table 1. It starts in state0. It changes state every 32 cycles. During the 32 cycles a singlenoOverlap bit collects the AND of all the dot advance bits for those 32cycles (noOverlap=dot advance for cycle 0, and noOverlap=noOverlap ANDdot advance for cycles 1 to 31).

TABLE 1 State machine for DRU output Next state No Overlap Output ValidComment state 0 X B 0 Startup state 1 1 1 B 1 Regular non-overlap 1 1 0B 1 A contains first 2 overlap 2 X Even A, 1 A contains second 3 even Boverlap B contains first overlap 3 X C, odd B 1 C contains first 1overlap B contains second overlap

The margin unit (MU) 457, in FIG. 52, is responsible for turning advancedot and advance line signals from the dither matrix access unit (DMAU)448 into general control signals based on the page margins of thecurrent page. It is also responsible for generating the end of pagecondition. The MU keeps a counter of dot and line across the page. Bothare set to 0 at the beginning of the page. The dot counter is advancedby 1 each time the MU receives a dot advance signal from the DMAU. Whenthe MU receives a line advance signal from the DMAU, the line counter isincremented and the dot counter is reset to 0. Each cycle, the currentline and dot values are compared to the margins of the page, andappropriate output dot advance, line advance and within margin signalsare given based on these margins. The DMAU contains the only substantialmemory requirements for the HCU.

Apart from being implicitly defined in relation to the printable pagearea, each page description is complete and self-contained. There is nodata stored separately from the page description to which the pagedescription refers. PEC relies on dither matrices and tag structures tohave already been set up, but these are not considered to be part of ageneral page format.

The page description consists of a page header which describes the sizeand resolution of the page, followed by one or more page bands whichdescribe the actual page content.

Table 2 shows the format of the page header.

TABLE 2 Page header format Field format Description Signature 16-bitPage header format signature. integer Version 16-bit Page header formatversion integer number. structure size 16-bit Size of page header.integer target resolution (dpi) 16-bit Resolution of target page. Thisis integer always 1600 for the present printer. target page width 16-bitWidth of target page, in dots. integer target page height 16-bit Heightof target page, in dots. integer target left margin 16-bit Width oftarget left margin, in integer dots. target top margin 16-bit Height oftarget top margin, in integer dots. tag flags 16-bit Bit 0 specifieswhether to integer generate tags for this page (0 = no, 1 = yes). Bit 1specifies the tag orientation (0 = portrait, 1 = landscape). Bit 2specifies whether the fixed tag data should be redundantly encoded byPEC or directly used (0 = directly use, 1 = encode). Bit 3 specifieswhether the variable tag data should be redundantly encoded by PEC ordirectly used (0 = directly use, 1 = encode). The remaining bits arereserved. fixed tag data 128-bit This is only valid if the generateinteger tags flag is set (bit 0 of tag flags). If bit 1 of tag flags isclear, then the lower 120 bits of fixed tag data contain the pre-encodedfixed data. If bit 1 of tag flags is set, then the lower 40 bits containthe unencoded fixed data that is to be encoded by PEC. The upper 8 bitsare reserved. black scale factor 16-bit Scale factor from black bi-levelinteger resolution to target resolution (must be 1 or greater). blackpage width 16-bit Width of black page, in black integer pixels. blackpage height 16-bit Height of black page, in black integer pixels.contone color space 16-bit Defines the number of contone integer JPEGchannels. Typically 3 or 4 for CMY vs CMYK. contonel scale factor 16-bitScale factor from contone channel integer 1 resolution to targetresolution (must be 1 or greater) contone 1 page width 16-bit Width ofcontone page, in integer contone 1 pixels. contone 1 page height 16-bitHeight of contone page, in integer contone 1 pixels. contone 2 scalefactor 16-bit Scale factor from contone channel integer 2 resolution totarget resolution (must be 1 or greater) contone 2 page width 16-bitWidth of contone page, in integer contone 2 pixels. contone 2 pageheight 16-bit Height of contone page, in integer contone 2 pixels.contone 3 scale factor 16-bit Scale factor from contone channel integer3 resolution to target resolution (must be 1 or greater) contone 3 pagewidth 16-bit Width of contone page, in contone integer 3 pixels. contone3 page height 16-bit Height of contone page, in contone integer 3pixels. contone 4 scale factor 16-bit Scale factor from contone channelinteger 4 resolution to target resolution (must be 1 or greater) contone4 page width 16-bit Width of contone page, in contone integer 4 pixels.contone 4 page height 16-bit Height of contone page, in contone 4pixels.

The page header contains a signature and version which allow the printengine to identify the page header format. If the signature and/orversion are missing or incompatible with the print engine, then theprint engine can reject the page. The contone color space defines howmany contone layers are present, which typically is used for definingwhether the contone layer is CMY or CMYK. The page header defines theresolution and size of the target page. The black and contone layers areclipped to the target page if necessary. This happens whenever the blackor contone scale factors are not factors of the target page width orheight. The target left and top margins define the positioning of thetarget page within the printable page area.

The tag parameters specify whether or not Netpage tags should beproduced for this page and what orientation the tags should be producedat (landscape or portrait mode). The fixed tag data is also provided.

The black layer parameters define the pixel size of the bi-level blacklayer, and its integer scale factor to the target resolution. Thecontone layer parameters define the pixel size of each of the fourcontone layers and their integer scale factor to the target resolution.

Table 3 shows the format of the page band header.

TABLE 3 Page band header format Field format description Signature16-bit Page band header format integer signature. Version 16-bit Pageband header format version integer number. Structure size 16-bit Size ofpage band header. integer Black band height 16-bit Height of black band,in black integer pixels. Black band data size 32-bit Size of black banddata, in bytes. integer Contone band height 16-bit Height of contoneband, in integer contone pixels. contone band data size 32-bit Size ofcontone band data, in integer bytes. dither matrix select map 32-bitSize of dither matrix select map band data size integer band data, inbytes. If the size = 0 only one dither matrix is used. Tag band datasize 32-bit Size of unencoded tag data band, integer in bytes. Can be 0which indicates that no tag data is provided.

The black (bi-level) layer parameters define the height of the blackband, and the size of its compressed band data. The variable-size blackdata follows the page band header. The contone layer parameters definethe height of the contone band, and the size of its compressed pagedata, consisting of the contone color data and the associated bi-leveldither matrix select map. The variable-size contone data follows theblack data. The variable-size bi-level dither matrix select map datafollows the contone data.

The tag band data is the set of tag data half-lines as required by thetag encoder. The format of the tag data is found below. The tag banddata follows the dither matrix select map.

Table 4 shows the format of the variable-size compressed band data whichfollows the page band header.

TABLE 4 Page band data format Field format description black data G4FaxCompressed bi-level black data. bytestream contone data JPEG Compressedcontone CMYK or bytestream CMY data. dither matrix select map G4FaxCompressed bi-level dither matrix bytestream select map data. tag datamap bitmap Tag data format. See Section 9.2.2.

Each variable-size segment of band data is aligned to an 8-byteboundary.

The tag encoder (TE) 430 in FIG. 50, provides functionality fortag-enabled applications, and it typically requires the presence of IRink at the print head (although K ink or other might be used for tags inlimited circumstances). The TE encodes fixed data for the page beingprinted, together with specific tag data values into anerror-correctable encoded tag which is subsequently printed in infraredor black ink on the page. The TE might place tags on a triangular grid(see FIG. 55), allowing for both landscape and portrait orientations.Basic tag structures are rendered at 1600 dpi, while tag data might beencoded as arbitrarily shaped macrodots (with a minimum size of 1 dot at1600 dpi).

The TE takes the following as input:

-   -   A portrait/landscape flag    -   A template defining the structure of a single tag    -   A number of fixed data bits (fixed for the page)    -   A flag that defines whether or not to redundantly encode the        fixed data bits or whether to treat the bits as already having        been encoded    -   A number of variable data bit records, where each record        contains the variable data bits for the tags on a given line of        tags    -   A flag that defines whether or not to redundantly encode the        variable data bits or whether to treat the bits as already        having been encoded.

The output from the tag encoder (TE) is a 1600 dpi bi-level layer ofwhere tag data should be printed. The output is via a 1-bit wide FIFO447 (in FIGS. 50 and 52) which is in turn used as input by the HCU 429in FIG. 50. The tags are subsequently preferably printed with aninfrared-absorptive ink that can be read by a tag sensing device. Sinceblack ink can be IR absorptive, limited functionality can be provided onoffset-printed pages using black ink on otherwise blank areas of thepage—for example to encode buttons. Alternatively an invisible infraredink can be used to print the position tags over the top of a regularpage. However, if invisible IR ink is used, care must be taken to ensurethat any other printed information on the page is printed ininfrared-transparent CMY ink, for black ink will obscure the infraredtags. The monochromatic scheme is preferred to maximize dynamic range inblurry reading environments.

When multiple PEC chips are used for printing the same side of a page,it is possible that a single tag will be produced by two PEC chips. Thisimplies that the tag encoder must be able to print partial tags.

Since the tag encoder (TE) outputs 1600 dpi bi-level data, the internalworkings of the TE are completely hidden from the half-toner/compositorunit (the user of tag data).

Even though the conceptual implementation of the tag encoder (TE) allowstags to have a variable structure as well as fixed and variable datacomponents, this implementation of the TE does impose range restrictionson certain encoding parameters. Table 5 lists the encoding parameters aswell as the range restrictions. However, these restrictions are a directresult of buffer sizes and the number of addressing bits, chosen for themost likely encoding scenarios. It is a simple matter to adjust thebuffer sizes and corresponding addressing to allow arbitrary encodingparameters in other implementations.

TABLE 5 Encoding parameters maximum value imposed Name Definition by TEW page width 12 inches S tag size minimum is 2 mm × 2 mm N number ofdots in each dimension 384 dots of the tag (minimum of 92 dots given E)E Redundancy encoding for tag data Reed-Solomon GF(2⁴) at 5:10 D_(F)size of fixed data (unencoded)  40 bits R_(F) size of redundancy encodedfixed 120 bits data D_(v) size of variable data (unencoded) 120 bitsR_(v) size of redundancy encoded 360 bits variable data T tags per pagewidth 152 (allows for packed 2 mm × 2 mm tags) M Macrodot size Minimumis 1 dot

Of particular note is the fixed and variable data component in each tag.The fixed data component is the part of tag data that does not change(different to the part of the tag structure that does change). The fixeddata is either read by the PEC chip in its unencoded form and encodedonce within PEC, or it can is read and used as-is (the fixed data shouldtherefore be redundantly encoded externally). The variable data bits arethose data bits that are variable for each tag, and are as with fixeddata, are redundancy encoded inside the TE as required or used as-is.

The mapping of data bits (both fixed and variable) to redundancy encodedbits relies heavily on the method of redundancy encoding employed.Reed-Solomon encoding was chosen for its ability to deal with bursterrors and effectively detect and correct errors using a minimum ofredundancy. Reed Solomon encoding is discussed in Lyppens, H.,“Reed-Solomon Error Correction”, Dr. Dobb's Journal Vol. 22, No. 1,January 1997, Rorabaugh, C, Error Coding Cookbook, McGraw-Hill 1996, andWicker, S., and Bhargava, V., Reed-Solomon Codes and their Applications,IEEE Press 1994.

In the present implementation of the tag encoder (TE) is usedReed-Solomon encoding over the Galois Field GF(2⁴). Symbol size is 4bits. Each codeword contains 15 4-bit symbols for a codeword length of60 bits. Of the 15 symbols, 5 are original data (20 bits), and 10 areredundancy bits (40 bits). The 10 redundancy symbols mean that we cancorrect up to 5 symbols in error.

The total amount of original data per tag is 160 bits (40 fixed, 120variable). This is redundancy encoded to give a total amount of 480 bits(120 fixed, 360 variable) as follows:

-   -   Each tag contains up to 40 bits of fixed original data.        Therefore 2 codewords are required for the fixed data, giving a        total encoded data size of 120 bits. Note that this fixed data        only needs to be encoded once per page.    -   Each tag contains up to 120 bits of variable original data.        Therefore 6 codewords are required for the variable data, giving        a total encoded data size of 360 bits.

The TE writes a bi-level tag bitstream to the bi-level tag FIFO. The TEis responsible for merging the encoded tag data with the basic tagstructure, and placing the dots in the output FIFO in the correct orderfor subsequent printing. The encoded tag data is generated from theoriginal data bits on-the-fly to minimize buffer space.

In FIG. 55 is seen the placement of tags for portrait and landscapeprinting. The TE preferably places tags 488 on the page in a triangulargrid arrangement, 488,489,490, accounting for both landscape 492 andportrait orientations 491. The triangular mesh of tags 488,489,490combined with the restriction of only two printing orientations(landscape and portrait) and no overlap of columns or rows of tags meansthat the process of tag placement is greatly simplified.

In FIG. 56 is seen the general case for placement of tags thereforerelies on a number of parameters. For a given line of dots, all the tagson that line correspond to the same part of the general tag structure.The triangular placement can be considered as alternative lines of tags,where one line of tags is inset by one amount in the dot dimension, andthe other line of dots is inset by a different amount. The dot inter-taggap 493 is the same in both lines of tag, and is different from the lineinter-tag gap 494.

The parameters are more formally described in Table 6 and Table 7. Notethat only one set of parameters are required—those for portraitprinting. If the orientation changes from portrait to landscape, thentag height and tag width parameters, and general dot and line parametersare simply interchanged.

TABLE 6 Tag placement parameters Parameter Description RestrictionsTagHeight The number of dot lines in minimum 1 a tag's bounding boxTagWidth The number of dots in a minimum 1 single line of the tag'sbounding box. The number of dots in the tag itself will vary dependingon the shape of the tag, but the number of dots in the bounding box willbe constant (by definition). Dot inter-tag gap The number of dots fromminimum = 0 the edge of one tag's bounding box to the start of the nexttag's bounding box, in the dot direction. Line inter-tag gap The numberof dot lines minimum = 0 from the edge of one tag's bounding box to thestart of the next tag's bounding box, in the line direction. StartPosition The Current Position see TABLE 10 Record (see TABLE 10) for thestart of the first row of dots on the page (or strip if multiple PECsare used) and the first row of tags. To increase the size of the non-tagged section beyond the size of the inter-tag gap, use non-printedtags. AltTagLinePosition The Current Position see TABLE record for thestart of the alternate row of tags. The dot para- meter is used forportrait mode printing, and the line parameter is used for landscapemode printing.

TABLE 7 Current position record Name Description TagStateDot 0 = ininter-tag gap 1 = in tag TagStateLine 0 = in inter-tag gap 1 = in tagLocalOffsetDot Current dot position within the inter-tag gap or tag,minimum = 0 LocalOffsetLine Current line position within the inter-taggap or tag, minimum = 0

The TE makes use of several specific data structures:

-   -   a TEOrientation flag, that determines whether the page is being        printed using portrait or landscape tag placement rules.    -   a tag format structure. A template detailing the composition of        a generic tag in terms of fixed tag structure, variable data        bits and fixed data bits. It is composed of a number of tag line        structures, one for each 1600 dpi line in the tag. There are two        tag format structures—one for portrait and one for landscape        printing.    -   a fixed tag data buffer. Contains the redundancy encoded fixed        data component for all tags on the page (or part of a page when        multiple PEC chips are used).    -   a TagIsPrinted flag. Specifies whether a particular tag is to be        printed or not. Directs the encoder whether to ignore the tag        format structure and simply output no tag.    -   a half-line tag data buffer. Contains the unencoded data and        TagIsPrinted flags for the tags in half of a given line of tags        (a line is the width of the strip printed by this PEC chip). If        only part of a tag is printed by this PEC then the whole tag's        data must be present.    -   a variable tag data buffer. Contains the redundancy encoded        variable data for a single tag.

The data structures are described in more detail below. Note that thesizes of the various structures are based on the tag encoding parametersas listed in Table 5. For different sets of encoding parameters thesizes of the structures and the corresponding number of address bitsshould be appropriately changed.

The TE supports both landscape and portrait printing. The mode iscompletely independent of the length of the printhead connected to thePEC. Given correct paper feed, a 12 inch printhead can print Letter andA4 pages in both landscape and portrait, and multiple PEC chips can becombined to produce arbitrary sized pages. As a result the TE contains aflag to determine the orientation of the tags.

TEOrientation is therefore a 1 bit flag with values as shown in Table 8.

TABLE 8 TE Orientation Register Values Value Description 0 Landscape 1Portrait

Each 10-bit entry is interpreted independently as described by Table 9,and has no reliance on state information. This is important so thatrandom access to the entries is possible, especially during therendering of one side of a partial tag (spread over 2 PECs).

TABLE 9 Interpretation of 10-bit entry in Tag Line Structure bit 9Interpretation 0 This dot is part of the basic tag structure. Bit 8contains the dot output value. The remaining 8 bits are reserved andshould be set to 0. 1 This dot is derived from the data part of the tag.The lower 9 bits are used to determine the actual data bit to use. Ifthe upper 2 bits of the address are set, the remaining 7 bits are usedto address the 120 bits of encoded fixed data for the page. If the upper2 bits of the address are not both set, the full 9 bit address is usedto address the 360 bits of encoded variable data for the tag.

Since the Tag Format Structure (TFS) is line based, we have two suchstructures stored in the external DRAM—one for portrait orientation, andone for landscape orientation printing. The TEOrientation flagdetermines which of the two will be used. The two tag format structuresare supplied by an external process, are stored in the external DRAM,and therefore can be arbitrarily different. In practice however, theyare the same tag rotated through 90 degrees. The total memory requiredby a single TFS is 3840×TagHeight bits. The maximum amount of memoryrequired is for a tag of height 384, and totals 180 KBytes. A maximumtotal of 360 KBytes is therefore required for the two orientations.

As seen in FIG. 55, for a given line of dots, all the tags on that linecorrespond to the same tag line structure. Consequently, for a givenline of output dots, a single tag line structure is required, and notthe entire TFS. Double buffering allows the next tag line structure tobe fetched from the TFS in DRAM while the existing tag line structure isused to render the current tag line. Reading a line of tag structuredata consequently consumes the same DRAM bandwidth regardless of theorientation. The entire TFS might be stored on the PEC chip, in whichcase the rotation could be performed on-the-fly. The memory requirementsfor the TFS is therefore a double buffered tag line structure on chip(totalling 3840 bits×2=7,680 bits, or 960 bytes), and up to 360 KBytesin the external DRAM for the portrait TFS and landscape TFS. In terms ofbandwidth, the writing of the portrait TFS and landscape TFS only has tobe done once, so is not an issue. Reading the appropriate TFS duringprinting however, is an issue. Assuming a worst case of adjacent tags,there is a need to read a tag line structure each output line. Each tagline structure is 480 bytes. For a maximum print speed of 30,000 linesper second, the TFS access amounts to 13.8 MB/sec.

The fixed tag data buffer is a 120-bit data buffer, addressed by 7 bits.The buffer holds the encoded fixed component of the tag data for thepage. The fixed tag data buffer is written to once per page eitherdirectly from the 120 bits of original fixed data input or after thelower 40 bits of original fixed data has been Reed-Solomon encoded.

A TagIsPrinted flag specifies whether or not a particular tag should beprinted. Only a single bit, this flag is double buffered for a total of2 bits. Double buffering allows the TagIsPrinted flag for the next tagto be determined while the current tag is being rendered. TagIsPrintedis therefore a 1 bit flag with values as shown in Table 10.

TABLE 10 TagIsPrinted register values Value Description 0 Don't printthe tag. Ignore the TFS as well as tag fixed and variable data values.Output 0 for each dot within the tag bounding box. 1 Print the tag asspecified by the various tag structures.

A Half-Line Tag Data Buffer contains the unencoded variable tag data forup to a half the tags on a line. Since each line can contain a maximumof 152 tags (a tag size of 2 mm×2 mm closely packed over a length of 12inches), each half-line tag buffer contains at most 76 tags. 128 bitsare allocated to each tag 495, 496, 497 and so on as shown in FIG. 55:120 bits of unencoded data 501, a 1 bit TagIsPrinted flag 498, a 1 bitLastTagOfHalfLine flag 499, and 6 reserved bits (set to 0) 500. The sizeof a single buffer is therefore 9728 bits (1216 bytes). The allocationof 1 bit to the TagIsPrinted flag 498, instead of having a magic valuefor the unencoded data (eg 0) means that the unencoded data is 120 bitsof completely unrestricted data.

Rather than double buffering an entire line of tag data, we triplebuffer a half line of tag data. This saves 1216 bytes (compared to thedouble buffered full tag line), but comes with a timing restriction inthat instead of having an entire line time to read the full tag line,the half-line tag data must be read in half a dotline. Note that it isimportant to have three half-line buffers and not just two. With onlytwo half-line buffers the same tag data needs to be re-read as a givenset of tags extends over multiple dot lines. The triple buffer allowsthe same two half-line tag buffers to be used multiple times (once foreach line of the tag) without having to be re-read from DRAM. The thirdhalf-line tag buffer is used to load the first half of the nexttag-line's data, during the processing of the current set of tags, andis used to load the second half of the next tag-line's data during theprocessing of the first half of the next tag-line. Note that a giventag-line's data is only read once during the entire print process.Consequently a 1-bit FirstTimeProcessed flag is associated with eachhalf-line buffer to specify if the tags on this half-line have beenprocessed before. The first time a given half-line is processed, thenext half-line buffer is loaded from DRAM.

The tag data is arranged in DRAM in terms of half-lines. If there are Ntags on a given line, each half-line stored in DRAM contains the datafor N/2 tags. If N is odd, one of the half-lines will contain 1 less tagthan the other. The LastTagOfflalfLine flag will be set in tag N/2 forone half line, and tag (N/2−1) for the other. Regardless, the offsetfrom one tag half-line to the next is the same in both cases. Portraitand landscape pages balance each other out in terms of total number oftags. Assuming a worst case of adjacent 2 mm×2 mm tags, there are 76tags per half-line, and for an 8.5 inch long page there are 107 tags inthe line dimension. The size of the entire data in DRAM is therefore1216×2×10⁸=255 KBytes. For a print speed of 1 page per second, thebandwidth to DRAM is therefore 255 KB/sec. For a maximum print speed of30,000 lines per second, the TFS access amounts to approximately 561KBytes/sec.

The variable tag data buffer holds the 360 bits of encoded variable datafor a single tag. The TE double buffers the variable tag data buffer fora total of 720 bits. Double buffering allows the raw 120 bits ofvariable data for the next tag to be redundancy encoded (if required)and stored in one variable tag data buffer while the other is being usedto generate dots for the current tag. Note that if the variable tag datais not encoded by PEC, only the first 120 bits of the 360 variable databits are valid, and it is the responsibility of the external pageprovider to ensure that the 120 bits of variable tag data haveappropriate redundancy encoding already applied.

The variable tag data buffer shown in FIG. 58 is the current tag'svariable data. While the dots for the current tag are being produced,the variable data for the next tag is being encoded to a second variabletag data buffer, as shown in FIG. 59.

Rather than store the entire tag format structure, or the variable tagdata for all tags, the data is loaded from the external DRAM in ajust-in-time way. Appropriate trade-offs are made between buffer sizesand transfer bandwidth. Processing ahead to ensure data is availablejust in time works occurs in both the dot and line directions.

-   -   As the dots for one tag are being generated in the dot        direction, the variable data component for the next tag are        being redundancy encoded into a second variable data buffer, and        the next tag's TagIsPrinted flag is being determined. Both of        these tasks involve reading the from the half-line tag data        buffer, and does not involve an access to the external DRAM.    -   The first time a half-line tag data buffer is used, the next        half-line of unencoded tag data is fetched from DRAM. Nothing is        read from DRAM when a half-line of tag data is used again. Since        there are 3 half-line tag buffers, two buffers can be used        multiple times for a single line of tags while the data for the        next half-line of tags is ready. Note that this allows each        tag's unencoded data to be read from DRAM only once.    -   While the dots for one line of tags are being produced, the next        line of the tag format structure is read from external DRAM.        This is only required if the current output line is actually        part of a tag. In the case of the last line of a tag the first        line of the tag is reread. Nothing is read while processing an        inter-tag line.

Table 11 summarizes the memory requirements for the TE, both in terms ofon-chip and off-chip (external DRAM) requirements.

TABLE 11 TE memory requirements On Chip Total Off Chip worst case NameRequirements (external DRAM) TE Orientation   1 bit — Tag FormatStructure  960 bytes 360 KBytes (total) Fixed tag data buffer  120 bits— TagIsPrinted flag   2 bits Half-line tag data buffers 3648 bytes 255KBytes (per page) Variable tag data buffer  720 bits — TOTAL 5018 bytes

At the highest level, a state machine in the TE steps through the outputlines of a page one line at a time, with the starting position either inan inter-tag gap or in a tag (a PEC may be only printing part of a tagdue to multiple PECs printing a single line). If the current position iswithin an inter-tag gap, an output of 0 is generated. If the currentposition is within a tag, the tag format structure is used to determinethe value of the output dot, using the appropriate encoded data bit fromthe fixed or variable data buffers as necessary. The TE then advancesalong the line of dots, moving through tags and inter-tag gaps accordingto the tag placement parameters. Once the entire line of output dots hasbeen produced, the TE advances to the next line of dots, moving throughtags and inter-tag gaps according to the tag placement rules for theline direction. An output dot must be generated each cycle in order tokeep up with other dot generating processes in the PEC. In pseudocode,the process is as follows. Note that the logic for accessing DRAM is notshown.

-   If (TEOrientation=Portrait)    -   maxTagComponentLine[0]=LineInterTagGap    -   maxTagComponentLine[1]=TagHeight    -   maxTagComponentDot[0]=DotInterTagGap    -   maxTagComponentDot[1]=TagWidth    -   startDotOffset[0]=StartPosition.LocalOffsetDot    -   startDotState[0]=StartPosition.TagStateDot    -   startDotOffset[1]=AltTagLinePosition.LocalOffsetDot    -   startDotState[1]=AltTagLinePosition.TagStateDot    -   CurrPos.TagStateLine=StartPosition.TagStateLine    -   CurrPos.LocalOffsetLine=StartPosition.LocalOffsetLine-   Else    -   maxTagComponentLine[0]=DotInterTagGap    -   maxTagComponentLine[1]=TagWidth    -   maxTagComponentDot[0]=LineInterTagGap    -   maxTagComponentDot[1]=TagHeight    -   startDotOffset[0]=StartPosition.LocalOffsetLine    -   startDotState[0]=StartPosition.TagStateLine    -   startDotOffset[1]=AltTagLinePosition.LocalOffsetLine    -   startDotState[1]=AltTagLinePosition.TagStateLine    -   CurrPos.TagStateLine=StartPosition.TagStateDot    -   CurrPos.LocalOffsetLine=StartPosition.LocalOffsetDot-   EndIf-   Stall until the RSEncoder's output TagReady flag is set-   transfer TagIsPrinted flag from RSEncoder to DotGenerator-   transfer variable tag data buffer from RSEncoder to DotGenerator-   send AdvanceTag signal to RSEncoder to begin encoding the next tag-   tagLineType=0-   LineCount=0-   While (LineCount<MaxLine)-   Do    -   CurrPos.TagStateDot=startDotState[tagLineType]    -   CurrPos.LocalOffsetDot=startDotOffset[tagLineType]    -   DotCout=0    -   While (DotCount<MaxDot)    -   Do        -   If (CurrPos.TagStateLine==inInterTagGap)            -   Write 0 to FIFO        -   Else            -   If (CurrPos.TagStateDot==in Tag)                -   Write (Decode                    TagLineStructure[CurrPos.LocalOffsetDot]) to FIFO            -   Else                -   Write 0 to FIFO            -   EndIf            -   increment CurrPos.LocalOffsetDot            -   If                (CurrPos.LocalOffsetDot>maxTagComponentDot[CurrPos.TagStateDot])                -   CurrPos.LocalOffsetDot=0                -   CurrPos.TagStateDot=((˜currPos.TagStateDot) OR                -    (dotInterTagGap==0))                -   If (CurrPos.TagStateDot==in Tag)                -    transfer TagIsPrinted flag from RSEncoder to                    DotGenerator                -    transfer variable tag data buffer from RSEncoder to                    DotGenerator                -    send AdvanceTag signal to RSEncoder to begin                    encoding the next tag                -   EndIf            -   EndIf        -   EndIf        -   increment DotCount    -   EndDo    -   increment lineCount    -   increment CurrPos.LocalOffsetLine    -   If        (CurrPos.LocalOffsetLine>maxTagComponentLine[CurrPos.TagStateLine])        -   CurrPos.TagStateLine=((˜currPos.TagStateLine) OR            (lineInterTagGap==0))        -   CurrPos.LocalOffsetLine=0        -   If (CurrPos.TagStateLine==inTag)            -   tagLineType=˜tagLineType        -   EndIf    -   EndIf-   EndDo

The outputting of a single bit based upon the position within the tagdepends on having access to the appropriate tag line structure, theencoded fixed and variable tag data for the current tag, and theTagIsPrinted flag for the current tag. Assuming that these have beenappropriately loaded, and assuming the encoding parameters of Table 5,the generation of a single tag dot can be seen in FIG. 58 in blockdiagram form.

In FIG. 59 is seen a block diagram of the encoder. The TE contains asymbol-at-a-time GF(2⁴) Reed-Solomon encoder 590. Symbol size is 4 bits.Each codeword contains 15 4-bit symbols for a codeword length of 60bits. Of the 15 symbols, 5 are original data (20 bits), and 10 areredundancy bits (40 bits). Since each tag contains 120 bits of variableoriginal data, 6 codewords are required for a total encoded data size of360 bits. The fixed tag data is also encoded using the same Reed-Solomonencoder. The fixed tag data is also encoded using the same Reed-Solomonencoder. The fixed data is constant over all tags for a given page (orstrip of a page if multiple PECs are used), so only needs to be set uponce before a print (or set of prints). The unencoded fixed data is 40bits in length. These 40 bits are encoded to produce 120 bits. To encodethe fixed data, the CPU loads the fixed data into the first 40 bits ofthe unencoded tag data buffer and then starts the state machine toencode two codewords. The resultant 120 bits in the variable tag dataare then transferred to the fixed tag data buffer where they will stayfor the printing of at least one page, and in most cases many pages. Ifthe fixed data is not to be encoded by PEC then all 120 bits of thefixed data are copied directly to the fixed tag data buffer. The statemachine 591 is responsible for producing the addressing and controlsignals for encoding the tag data. Table 13 shows the registers used toprogram the state machine 591.

The TagReady flag is cleared at 592 by the state machine 591 at startup,and subsequently whenever the AdvanceTag signal is received at 593. Theflag is set once the entire set of codewords has been appropriatelyReed-Solomon encoded. The TagReady flag allows external users of theencoded data to stall appropriately.

To produce an encoding of 5:10 symbols, the state machine 591 gates4-bit data at 595 from the appropriate half-line tag buffer 594 into thesymbol-width Reed-Solomon decoder 590. A clock-data signal is suppliedfor the first 5 clocks, and the inverse of that is supplied for the next10. This is repeated NumberOfCodewords times. 90 clocks are thereforerequired to encode the entire tag data (6 codewords×15 clocks). Afurther 2 clocks are required to skip over the remaining 8 bits, thustaking the total to 92 cycles. The state machine 591 sets the TagReadyflag at 592, and stalls until the Advance signal on 593 is given fromthe TE's high level process (the time taken for this signal to be givenwill depend on the width of the tag. A tag size of 92 gives a minimumdelay). On the first of these last 2 clocks, a WriteEnable signal isgenerated on 596 so that the TagIsPrinted flag 597 is set to the 1st bitof 4 read from the unencoded tag data buffer 594 (bit 121 of tag data).During the same clock, the 2nd bit of 4 is passed to the state machine.This 2nd bit, called LastTaglnHalfLine determines whether the tag justprocessed is in fact the last tag to be processed in the half-linebuffer.

The address generated by the state machine 591 for the half-line tagbuffer 594 is 14 bits. The high 2 bits select which of the 3 databuffers are addressed. The next 9 bits determine which 32-bit quantityto read from the buffer, and the lower 3 bits are used to determinewhich of the 8 sets of 4-bits should be selected. Of the 14 addressbits, the lower 12-bit address starts at 0, and increments each cycleuntil it has advanced 32 times. The counter then stalls until theAdvanceTag signal on 593 comes in from the high level encoding process.If however, the LastTaglnHalfLine flag is set (read as bit 122 from thelatest processed tag), then the lower 12-bit address is cleared to 0,the tag half-line buffer 2-bit index is updated, and the load processfor the next half-line of tag data from DRAM is potentially started.

The state machine 591 keeps a 10-bit TagLineCounter for the number ofhalf-lines processed for this full tag line. The TagLineCounter iscleared at startup, and then incremented each time the state machinefinishes encoding a tag whose LastTaglnHalfLine flag is set. When theTagLineCounter is incremented, the 10 bits are used to determine the newvalue for the half-line index as well as potentially resetting theTagLineCounter itself. When in the first half of the line (the lowestbit of TagLineCounter=0), the next half-line buffer will always be thesecond half-line of the same tag line. This simply means updating the2-bit index. When in the second half of the line (the lowest bit ofTagLineCounter=1), the next half line depends on whether we havefinished processing this tag line or not. If we have not finishedprocessing the tag line (the 9 highest bits of TagLineCounter don'tmatch either TagHeight or TagWidth, depending on the value inTEOrientation), the next half-line is the same as the previoushalf-line. If we have finished the tag line, the next half-line comesfrom the next line, and therefore we use the next tag line's half-linebuffer. Since we are starting a new tag line, the counter is cleared to0 as well. Table 12 shows the relationship between old and new counterand half-line buffer indexes.

TABLE 12 What to do when LastTagInHalfLine is set Upper bits of Lo bitof TagLineCounter = Current Next Index Clear TagLineCounter tag heightIndex Value Value Counter?  0¹⁰  x¹¹ 0 1 No 0 X 1 2 No 0 X 2 0 No  1¹² 00 2 No 1 0 1 0 No 1 0 2 1 No 1 1 0 1 Yes 1 1 1 2 Yes 1 1 2 0 Yes¹⁰signifies first half of line ¹¹don't care state ¹²signifies secondhalf of line

Whenever the index value changes, the old index is kept and theFirstTimeProcessed flag for the half-line buffer associated with the newindex is checked. If the FirstTimeProcessed flag is clear, nothing moreis done. However, if the FirstTimeProcessed flag is set, it is clearedand the process of reading the next set of data for the next half-linefrom DRAM into the half-line specified by the old index is started. TheFirstTimeProcessed flag for the half-line associated with the old indexis then set. The number of 32-bit words to be read from DRAM isspecified by the HalfLineSize register, as described in Table 13. Thecurrent address for reading tag half lines

is then incremented by HalfLineSize so that it is pointing at the nexthalf-line to be read. This scheme causes a single half-line to be readin anticipation at the end of the page. Since the data is not sent tothe page, it does not matter.

TABLE 13 Registers for manipulating tag's variable data ParameterDescription Typical Value DataSymbols The number of data symbols 5 in anoutput codeword RedundancySymbols The number of redundancy 10 symbols inan output codeword NumberOfCodeWords The number of codewords to 6 encodeHalfLineSize The number of 32-bit 304 quantities in a half- line ofvariable tag data to be loaded from DRAM EncodeSelect If this bit isset, then data is 1 Reed-Solomon encoded. If clear, the data is merelycopied.

CONCLUSION

The present invention has been described with reference to a preferredembodiment and number of specific alternative embodiments. However, itwill be appreciated by those skilled in the relevant fields that anumber of other embodiments, differing from those specificallydescribed, will also fall within the spirit and scope of the presentinvention. Accordingly, it will be understood that the invention is notintended to be limited to the specific embodiments described in thepresent specification, including documents incorporated bycross-reference as appropriate. The scope of the invention is onlylimited by the attached claims.

1. A controller for a printhead, the controller comprising an encoderfor encoding tags to be printed on a page, the encoder having: an inputat which to receive a tag structure template having at least onepredetermined mark position; an input at which to receive fixed databits; an input at which to receive variable data bits; and a dotgenerator which uses the input tag structure template, and fixed andvariable data bits for outputting, for at least one mark position of arespective tag, a single bit indicating if a dot is to be provided atthe at least one mark position, for the respective tag.
 2. A controlleraccording to claim 1, comprising a redundancy encoder for optionallyencoding the fixed and variable data bits.
 3. A controller according toclaim 2 wherein the redundancy encoder uses Reed-Solomon encoding.
 4. Acontroller according to claim 1 wherein tags are placed regularly on apage.
 5. A controller according to claim 4 wherein tags are placed in atriangular grid.